GB2192078A - Scheduling method for input/output units - Google Patents

Description

GB2192078A 1 SPECIFICATION data transfer time of one input/output unit is

performed at one schedule point; characterized Scheduling method for input/output units in that a next schedule point is set to be preceded by the pre-process time interval to a

Background of the Invention: 70 time at which the prefetch/postwrite data

Field of the Invention: transfer process scheduled at a present sche

The present invention relates to an input/out- dule point will end, and that at the next sche put scheduling method, and more particularly dule point, whether the prefetch/postwrite to a prefetch/postwrite scheduling method for schedule process for the input/output unit a plurality of input/outputs units where not 75 scheduled at the current point is to be con only start processes previous to data transfer tinued or the prefetch/postwrite schedule pro processes are performed off-line from a con- cess of another input/output unit is to be per troller but the start process times and stop formed is further determined depending upon times of the respective units may lie in a con- an operating situation.

stant distribution. 80 Brief Description of the Drawings:

Description of the Prior Art: Figure 1 is a processing flow chart showing

A conventional magnetic tape unit includes a an embodiment of the present; vacuum column, and can therefore perform the Figure 2 is an architectural diagram of a start process of a magnetic tape at high 85 computer system to which the present inven- speed with the vacuum column. In contrast, a tion is directed; cartridge type magnetic tape unit has the va- Figure 3 is a block diagram of a controller in cuum column, indispensable to the high-speed the system; start process of the magnetic tape unit, re- Figure 4 is a format diagram of a controller moved for the purposes of a lighter weight 90 management information part; and a smaller size. As regards the cartridge Figure 5 is a format diagram of an MT man type magnetic tape unit, therefore, a control agement information part; method quite similar to that of a disk unit has Figure 6 is a format diagram of a prefetch/ been proposed wherein the start process is postwrite schedule queue; performed in off-line fashion, and after the 95 Figure 7 is a diagram showing the basic start, the magnetic tape unit is reconnected concept of the present invention; with a controller at the stage at which data Figure 8 is a diagram for explaining a transfer has become possible. method of setting a next schedule point; and The cartridge type magnetic tape unit (here- Figure 9 is a flow chart showing the details inbelow, termed -MT unit") having the char- 100 of a partial process in Fig. 1.

acteristics as stated above has had the prob lem that, once the data transfer has ended, Detailed Description of the Preferred Embodi- process times required for stop, repositioning meffs:

and start processes are much longer than in First, the principle of the present invention the conventional magnetic tape unit including 105 will be described.

the vacuum column. In a case where the prefetch/postwrite schedule process of a certain MT unit has Summary of the Invention: been started, a start request for this MT unit

An object of the present invention is to pro- is first issued. That is, this MT unit must have vide an input/output scheduling method which 110 completed a repositioning process.

eliminates the problem of the prior-art system Meanwhile, this MT unit is an MT unit as stated above and by which, even in a case which fulfills either the condition (termed where the access rates of recurrence of re"Condition 1") that, since the last schedule spective input/output units are not uniform, a point of the last prefetch/postwrite process of data transfer path extended between the inpu- 115 this MT unit, the sum of the time interval of t/output units and a controller for controlling data transfer by other MT units with the chan them can be efficiently used, and the pre- nels and the idle time interval of a path for fetch/postwrite of data can be realized with data transfer with the channels exceeds the the smallest buffer size. total of time intervals required for the stop, The present invention for accomplishing 120 repositioning and start operations of the parti such an object consists in an input/output cular MT unit, or the condition (termed "Con scheduling method wherein, in a case where dition 2") that the amount of data transfer of for input/output units which perform pre-pro- the MT unit to-be-scheduled itself with the cesses of fixed time interval off-line from a channel since the aforementioned point of controller in advance of data transfer pro- 125 time exceeds a predetermined value.

cesses, a plurality of blocks are prefetched/ The amount of prefetch/postwrite data on postwritten between the input/output units this occasion shall be the amount of data and a buffer disposed in the controller, a which has been transferred between the parti schedule process for determining the pre- cular MT unit and the channel since the point fetch/postwrite amount and prefetch/postwrite 130 of the last prefetch/postwrite final schedule 2 GB2192078A 2 process of this MT unit. In this case, accord- present invention, they shall not be especially ingly, the next schedule point may be set at a referred to in the following embodiments. In time which is earlier by the time interval of addition, since known methods are used for the start process than the time of the end of the management of sections allocated to the the prefetch/postwrite data transfer process 70 respective MT units 14 and the management scheduled at the present schedule point. of empty sections, they shall not be especially Concretely, the prefetch/postwrite data explained here.

transfer process scheduled at the present A data transfer unit 22 executes the data schedule point is started later than the present transfer between the channel 12 and the schedule point by the start process time interbuffer 21. Besides, a data transfer unit 23 val, so that the next schedule point may be executes the data transfer between the IVIT set at a time which is later than the present units 14 and the buffer 2 1. The above two schedule point by a time interval required for data transfer units 22 and 23 are subject to the scheduled prefetch/postwrite data transfer the controls of the processor 20.

process. 80 A clock 24 indicates the present time. A If the condition 1 is satisfied at the present timer 25 turns "on" a timer flag 26 after a schedule point, the data of another IVIT unit is designate time designated by the processor prefetched/postwritten at the next schedule 20. A controller management information part point. 28 is an information part which is provided in In contrast, if the condition 1 does not hold 85 correspondence with the controller 13. On the at the present schedule point, the schedule other hand, MT management information parts process of the particular MT unit is performed 27 are information parts which are provided in even at the next schedule point. The later correspondence with the respective MT units schedule point at which the condition 1 has 14.

held is deemed the final schedule point of the 90 A data transfer path 29A and a control in single prefetch/postwrite process which is formation path 29B are provided between the performed while occupying the data transfer MT units 14 and the controller 13. The con path continuously. At the next schedule point trol information path 29B is used for the issue after the condition 1 has held, the prefetch/- of a start request for each MT unit 14, the postwrite schedule process of the other MT 95 issue of a stop/repositioning request, the re unit is initiated. ceipt of the notice of the completion of a Now, embodiments of the present invention start process, as well as the notice of the will be described in detail with reference to completion of repositioning, etc.

the drawings. The data transfer path 29A is used for the Fig. 2 is a diagram showing the architecture 100 transfer of data. Since the control information of a computer system to which the present path 29B and the data transfer path 29A can invention is directed. The computer system is operate independently, the start request can constructed of a CPU 10, a main storage 11, be issued for another IVIT unit 14 during the a channel 12, a controller 13, and at least data transfer with a certain MT unit 14.

two, cartridge type magnetic tape units (here- 105 Either the data transfer path 29A or the inbelow, termed -MT units") 14. control information path 29B may be used for Fig. 3 shows the internal arrangement of the the stop/ repositioning requests for the respec controller 13 and the connectional relationship tive IVIT units 14, and for the receipts of the thereof with the IVIT units. A processor 20 start completion notice and repositioning com executes the controls of data transfers with 110 pletion notice from the IVIT unit 14.

the channel 12 and the IVIT units 14, the man- Fig. 4 shows the format of the controller agement of a buffer 2 1, etc. The buffer 21 is mangement information part 28, The controller divided into a plurality of sections, which are management information part 28 is an infor dynamically allocated to and released from the mation part which stores therein information MT units 14. 115 items provided in correspondence with the In this embodiment, a system for construct- controller 13, and only the items directly perti ing the buffer 21 is not especially discussed nent to the present invention will be explained as a theme. Therefore, the size of the buffer here.

is assumed to be sufficient and a case where First, a prefetch/postwrite schedule pointer a data transfer process is interrupted because 120 30 points to the IVIT management information of the absence of any unoccupied area of the part 27 of the head MT unit 14 to which a buffer 21 shall not be supposed. It is also prefetch/postwrite schedule is directed. A pre assumed that, when an empty area has be- fetch/postwrite schedule pointer 31 points to come insufficient within a given section, each the MT management information part 27 of IVIT unit 14 secure a necessary number of 125 the tail MT unit 14 to which the prefetch/po sections anew, and that, when a certain sec- stwrite schedule is directed.

tion has become empty wholly, it release the An IVIT data transfer rate 32 denotes the section. data transfer process rate of each of the IVIT Since the area securing process and releas- units 14 connected to the controller 13. A ing process are not directly pertinent to the 130 data transfer impossibility time 33 denotes the 3 GB2192078A 3 minimum time interval required before the MT 500 changes dynamically. Since, however, this unit 14 having ended data transfer once initi- mode of operation is not directly pertinent to ates data transfer next, that is, the total time the present invention, it shall not be especially interval of the stop, repositioning and start referred to in the description of the embodi operations. 70 ments, and cases where the controller 13 re Although this embodiment will refer to a ceives a mount request and a rewind request case where the data transfer rates and data from the channel 12 will not be particularly transfer impossibility times of the respective explained.

IVIT units 14 are common, the present inven- There will be explained below a case where tion is effective even when these character- 75 a certain number of MT units whose car istics differ in the individual MT units. tridges are mounted are existent from the be Further, a prefetch/postwrite schedule flag ginning and where the set of these units is 34 turns "on" when the next prefetch/po- operating without any change.

stwrite schedule point has been set, The initial A read/write flag 43 indicates whether this value of the prefetch/postwrite schedule flag 80 MT unit 14 is under a read process or under 34 shall be "off ". a write process. When the first data transfer Fig. 5 shows the format of the MT manage- request has been accepted, the read/write flag ment information part 27. The MT managment 43 is set in a read status if the request is a information parts 27 are information parts read request, and it is set in a write status if which are disposed for the respective MT un- 85 the request is a write request. In this embodi its 14, and only items directly pertinent to the ment, however, the case where the set of the present invention will be explained here. IVIT units 14 in the prefetch/postwrite sche An item MTiD 40 is the identifier of the MT dule queue 500 does not change will be re unit 14, and it indicates which of the MT units ferred to as already stated, the value of the 14 this MT management information part 27 90 read/write flag 43 is assumed to be already belongs to. set.

A prefetch/postwrite back pointer 41 points A data amount in the buffer, 44 denotes to the MT management information part 27 of the amount in which the data of this MT unit the MT unit which is subjected to a prefetch/- 14 exists within the buffer.

postwrite schedule subsequently to this MT 95 An unscheduled data amount 45 is the unit 14. On the other hand, a prefetch/po- amount of data transfer which is added each stwrite front pointer 42 points to the MT time the data transfer occurs between the MT management information part 27 of the MT unit 14 and the channel 12, and which is unit which is subjected to a prefetch/postwrite cleared when the prefetch/postwrite schedule schedule previously to this MT unit 14. The 100 process of this IVIT unit 14 has been per relationship is illustrated in Fig. 6 as a preformed at a schedule point. However, in case fetch/postwrite queue 500; of the MT unit 14 which has started the read The IVIT management information part 27 process anew, the initial predictive value of a which the processor 20 subjects to the pre- prefetch data amount needs to be set in this fetch/postwrite schedule, lies at the head of 105 area.

the prefetch/postwrite schedule queue 500. When prefetch data has become null before When the prefetch/postwrite schedule process the initiation of the next prefetch, a prefetch of a certain MT unit 14 has ended, the proadjust data amount 46 is used for adjusting cessor 20 shifts the MT management informa- the prefetch data amount at the next prefetch.

tion part 27 of this MT unit to the tail of the 110 Before the explanation of a last prefetch/po prefetch/postwrite schedule queue 500. In stwrite final schedule time 47, the basic set seeking the MT unit to be subsequently sub- ting method of the prefetch/postwrite sche jected to the prefetch/postwrite schedule, the dule process in the present invention will be pointer pointing to the MT unit which fulfills somewhat described.

the condition is searched for from the head of 115 Fig. 7 shows the outline of this method. In the prefetch/postwrite schedule queue 500. the present invention, when the prefetch/po When it has been found out, the MT manage- stwrite schedule of a certain IVIT unit 14 is ment information part 27 of this MT unit is started, it is carried out several times until a shifted to the head of the prefetch/postwrite certain condition is fulfilled. At the schedule schedule queue 500. 120 point at which the condition has been fulfilled, Here, the set of the MT units 14 registered the schedule of this MT unit 14 is ended and in the prefetch/postwrite schedule queue 500 is switched to the prefetch/postwrite schedule is the set of the IVIT units whose cartridges process of another MT unit 14.

are mounted on a deck. In general, a mount The prefetch/postwrite data amount in the request for each IVIT unit 14 is issued dynami- 125 present invention is basically set at a data cally, and when the IVIT unit has ended oper- amount which is equal to the amount of data ating, it is subjected to a rewind process and transfer which has arisen between the IVIT unit is thereafter removed. 14 and the channel 12 since the last schedule Accordingly, the set of the MT units which point till the present schedule point. Thus as are registered in the prefetch/postwrite queue 130 illustrated in Fig. 7, when the certain MT nit 4 GB2192078A 4 (MTi) has fallen into a prefetch/postwrite Thereafter, the establishment of the condi- schedule again (a point 62 in Fig. 7) after the tion 1 is checked also at the next schedule prefetch/postwrite schedule thereof was once point 63, and the process of the prefetch/po switched to the other IVIT unit 14, the pre- stwrite schedule of this IVIT unit 14 is confetch/postwrite data amount of the certain MT 70 tinued until the condition 1 holds. At a sche- unit 14 becomes the amount of data having dule point subsequent to the schedule point at been transferred between this IVIT unit and the which the establishment of the condition 1 channel 12 since a schedule point (hereinbe- has been acknowledged, the prefetch/po low, called the "last prefetch/postwrite final stwrite schedule process is switched to the schedule point," and indicated at numeral 60 75 other IVIT unit 14.

in Fig. 7) immediately preceding a schedule In addition, the schedule point at which the point at which the schedule was switched to establishment of the condition 1 has been ac the other IVIT unit 14 in the last prefetch/po- knowledged becomes the last prefetch/po stwrite schedule process. stwrite final schedule point at the time at As stated before, once the IVIT unit 14 has 80 which the prefetch/postwrite schedule process ended the data transfer process, it cannot of this MT unit 14 is started again.

start the next data transfer process during the Referring back to Fig. 5, the last prefetch/ stop and repositioning processes. Accordingly, postwrite final schedule time 47 denotes a if the prefetch/postwrite process of another time which is obtained from the clock 24 at IVIT unit is feasible meantime, the data transfer 85 the prefetch/postwrite final schedule point.

path can be effectively utilized. A transferred data amount 48 is the amount As illustrated in Fig. 7, the time interval of of data which has been transferred with re- data transfer with respect to the channel 12 spect to the channel 12 since the aforemen till the present time since the last prefetch/po- tioned point. In case of executing the prefetch stwrite final schedule point can be divided into 90 of the IVIT unit 14 which has started the read the data transfer time of this IVIT unit 14 and process, a value enough to satisfy the pre that of the IVIT unit 14 other than this IVIT fetch/postwrite start condition needs to be unit. When an idle time is considered as a set as the transferred data amount 48.

transfer time concerning a virtual IVIT unit 14 An under-operation flag 49 indicates that which is not really existent, the schedule may 95 this IVIT unit 14 is under the stop or reposi be switched to the other MT unit 14 if the tioning operation.

condition ("Condition 1" stated before) holds A prefetch/postwrite data amount 50 de that the sum between the data transfer time notes the amount of data to be prefetched/ of the other IVIT unit 14 and the idle time is postwritten with respect to the IVIT unit 14.

greater than the total of the time intervals of 100 A wait flag 51 turns "on" when the IVIT the stop, repositioning and start processes. unit 14 under the read process is in a wait The data transfer time of the other IVIT unit status because of the absence of prefetch 14 and the idle time may, in effect, be re- data.

placed with a time interval obtained in such a A schedule suspension condition flag 52 way that the data transfer time of the IVIT unit 105 turns "on" when the condition 1 has held.

14 to be scheduled is subtracted from a time The respective initial values of the under interval elapsed till the present time since the operation flag 49, the wait flag 51 and the last prefetch/postwrite final schedule point. In schedule suspension condition flag 52 shall be the ensuing description, this measure shall be 1. off."

used. 110 Referring now to Fig. 8, the time relation If the condition 1 holds at the present sche- ship in which the prefetch/postwrite schedule dule point 62, the data amount equal to the process in the present invention and the pro amount of data transfer which has arisen with cess of the scheduled transfer of prefetch/po respect to the channel 12 since the last pre- stwrite data are executed will be described.

fetch/postwrite final schedule point 60 is set 115 In Fig. 8, a schedule point 1 is assumed the as the prefetch/postwrite schedule data point at which an IVIT unit 14 (MTi) different amount, and the schedule process may be from an IVIT unit 14 (MTh) having been sche switched to the other IVIT unit 14 at the next duled at a schedule point 0 is scheduled.

schedule point 63. At the schedule point 1, accordingly, the However, even the MT unit 14 for which 120 prefetch/postwrite queue 500 is manipulated the condition 1 does not hold falls into the to find out the IVIT unit 14 which fulfills the last prefetch/postwrite schedule process in prefetch/postwrite condition 1. Processing to some cases. The reason therefor is that, un- be stated below indicates contents which are less the IVIT 14 for which the condition 1 executed when the IVIT unit 14 fulfilling the does not hold is made the object of the pre- 125 condition has been found out.

fetch/postwrite schedule, the required size of Here, the processor 20 first determines the the buffer 21 will become infinity. On this ocprefetch/postwrite data amount of this IVIT casion, the prefetch/postwrite schedule of the unit 14. Subsequently, it issues a start reauest particular MT unit 14 is performed even at the for this IVIT unit 14. Thus, as illustrated in Fig.

next schedule point 63. 1308, the transfer process of the prefetch/poGB2192078A 5 stwrite data is started with a delay corre- vention is also effective in the case where the sponding to a start time interval from the pre- set of the MT units 14 whose cartridges are sent time. mounted changes, that is, where the set of If, on this occasion, the condition 1 holds, it the MT units 14 of the prefetch/postwrite is necessary as already explained to perform 70 schedule queue 500 changes.

the prefetch/postwrite schedule of another MT At a step 72, predetermined processing be unit (MTj) and issue a start request at a sche- tween the processor 20 and the channel 12 is dule point 2. Accordingly, for the purpose of executed. Further, at a step 73, the MT man continuously performing the prefetch/postwrite agement information part 27 of the MT unit data transfer process scheduled at the sche- 75 14 which is the object of the input/output dule point 1 and the prefetch/postwrite data request is referred to, and at a step 74, transfer process to be scheduled at the sche- whether or not the request is the read request dule point 2, this schedule point 2 needs to and whether or not the data amount 44 within be set earlier by the start process time than the buffer is null are checked. If these condi the point of time at which the prefetch/potions hold, the wait flag 51 is turned "on" at stwrite data transfer process scheduled at the a step 75, whereupon the control flow returns schedule point 1 ends, as illustrated in the to the step 65.

figure. In a case where the above conditions do This prefetch/postwrite data transfer pro- not hold at the step 74, a step 76 secures an cess is started later by the start process time 85 unoccupied section within the buffer 21, if interval than the schedule point 1. Therefore, necessary, in case of the write request and the schedule point 2 may be set later by a issues a data transfer request for the data time interval which is required for transferring transfer unit 22.

a prefetch/postwrite data amount scheduled at Next, there will be described the case where the schedule point 1. 90 the processor 20 has received the process In a case where the condition 1 does not completion notice from the data transfer unit hold, the MT unit 14 scheduled at the sche- 22. In this case, the processor 20 receives dule point 1 is scheduled at the schedule po- the amount of transferred data from the data int 2. In this case, it is not especially proble- transfer unit 22.

matic to set the schedule point 2 at the same 95 At a step 77, predetermined processing be time as in the case where the condition 1 has tween the processor 20 and the channel 12 is held. Therefore, the next schedule points shall executed, whereupon various parameters are be set at similar times here., updated in accordance with the data transfer Now, the processing flow of the processor amount. Concretely, this value is added to the 20 is shown in Fig. 1. 100 unscheduled data amount 45 and the trans The processor 20 starts operating when it ferred data amount 48. Further, in the case of has received an input/output process request the write process, the data amount 44 within from the channel (step 65), when it has re- the buffer is increased by the data transfer ceived a transfer completion notice from the amount, whereas in the case of the read pro data transfer unit 22 (step 66), when it has 105 cess, it is decreased by the data transfer received a process completion notice from the amount. Moreover, processing for the man MT unit 14 (step 67), when it has received a agement of the buffer 21, which is necessi transfer completion notice from the data trans- tated by the data transfer process, is exe fer unit 23 (step 68), or when the timer flag cuted by a known method. Thereafter, the 26 is "on" (step 69). 110 control flow returns to the step 65.

Further, in a case where a schedule is im- Next, there will be described the case where mediately possible when the MT unit 14 fulfill- the processor 20 has received the process ing the prefetch/postwrite start condition is completion notice from the MT unit 14.

existent at present, concretely, in a case Although the processor 20 receives various where the prefetch/postwrite schedule flag 34 115 notices from the MT units 14, the receipts of is "off," steps (shown in Fig. 9) for seeking a start completion notice and a repositioning this MT unit 14 satisfying the condition are completion notice which are directly pertinent executed (steps 70, 71). to the present invention will be explained First, there will be described the case where here. By the way, the completion notices are the processor 20 has received the input/out120 received through the control information path put process request from the channel 12. Ak 29B.

though the processor 20 receives various in- At a step 78, the sort of the above comple put/output requests from the channel 12, only tion notice is decided. In the case where the data transfer requests, namely, a read request repositioning completion notice has been re- and a write request pertinent to the present 125 ceived, the control flow proceeds to a step invention shall be considered here. Also, it is 79, at which the MT management information assumed here that a cartridge has already part 27 corresponding to the MT unit 14 from been mounted as to the MT unit 14 which is which this notice has been received is found to receive the data transfer request, out, and the under-operation flag 49 is turned As stated before, however, the present in- 130 "off", whereupon the control flow returns to 6 GB2192078A 6 the step 65. lowing equation (1) holds is checked:

On the other hand, in the case where the start completion notice has been received, the [(present time)-(last prefetch/postwrite final control flow proceeds to a step 80, at which schedule time 47)] the IVIT management information part 27 cor- 70 responding to the IVIT unit 14 from whichh transferred data amount this notice has been received is found out, and predetermined processing with respect to IVIT data transfer rate the IVIT unit 14 is executed according to the read/write flag 43, whereupon a request for 75 _,(data transfer impossiblity time interval the transfer of data corresponding to one where the IVIT data transfer rate includes an block is issued to the data transfer unit 23. overhead 01, and the data transfer impossibil Thereafter, the control flow returns to the ity timeinterval includes an overhead 02 step 65. Here, the present time shall be obtained from Next, there will be described the case where 80 the clock 24.

the process completion notice from the data In a case where the above equation (1) transfer unit 23 has been received. holds, a step 90 sets the present time at the In this case, the amount of data transferred last prefetch/postwrite final schedule time 47 by this data transfer is received from the data and brings the transferred data amount 48 to transfer unit 23. At a step 81, operations for 85 zero. Further, the schedule suspension condi the management of the buffer 21 which are tion flag 52 is turned "on".

necessitated by this data transfer process are Subsequently, the prefetch/postwrite data executed by a known method, and the pre- amount is updated. Herein, at a step 9 1, the fetch/postwrite data amount 50 is decreased unscheduled data amount 45 is decided, and by the data transfer amount. 90 when it is zero, there is no data amount to be At a step 82, the data amount 44 within added. Therefore, for the purpose of switch the buffer is increased by the above data ing the prefetch/postwrite to another IVIT unit amount in the case of the read process, 14, the transferred amount 48 and the last whereas it is decreased by the same amount prefetch/postwrite final schedule time 47 are in the case of the write process. 95 updated at a step 95, which is followed by Subsequently, at a step 83, whether or not the step 96.

the prefetch/postwrite is further continued is On the other hand, in a case where the decided according to the value of the pre- unscheduled data amount 45 is decided to be fetch/postwrite data amount 50. Subject to non-zero by the decision of the step 9 1, the the continuation, a step 84 executes predeter- 100 value of the unscheduled data amount 45 is mined processing with the IVIT unit 14 and added to the prefetch/postwrite data amount thereafter issues a request for the transfer of 50 at a step 92.

one further block to the data transfer unit 23. Subsequently, a step 93 turns "off" the Subject to the dicontinuation, a step 85 is- timer flag 26 and starts the timer 25 in order sues the stop and repositioning requests to 105 to set the next schedule point. Besides, the the IVIT unit 14 and turns "on" the under- timer 25 is set so that the timer flag 26 may operation flag 49 through the control informa- turn "on" later than the present time by a tion path 29B. time interval indicated by the following equa Further, a step 86 checks whether or not tion (2):

the wait flag 51 is "on." If it is "on" in this 110 case, the corresponding IVIT unit 14 is waiting (unscheduled data amount) for the read request. At a step 87, therefore, +03 (2) the wait flag 51 is turned "off," and predeter- - (MT data transfer rate) mined processing with respect to the channel 12 is executed, whereupon the data transfer 115 where 03 denotes an overhead time interval.

unit 22 is started in order to transfer one Thereafter, the unscheduled data amount 45 block of data to the channel. is cleared at a step 94, whereupon the control Next, there will be described operations in flow returns to the step 65.

the case where the timer flag 26 has turned At the step 96, the prefetch/postwrite "on." 120 schedule flag 34 is turned "off." Further, the At a step 88, the MT management informa- MT information management part 27 of this tion part 27 of the IVIT unit 14 to be sche- IVIT unit 14 is shifted to the tail of the pre duled, which lies at the head of the prefetch/- fetch/postwrite schedule, and the schedule postwrite schedule queue 500, is derived, and suspension condition flag 52 is turned "off."

whether or not the schedule suspension condi- 125 Thereafter, the control flow proceeds to the tion flag 52 is "on" is checked. If the flag 52 step 71 in order that, to the end of perform is "on," the control flow proceeds to a step ing the prefetch/postwrite schedule process of 96. When it is "off," operations to be stated another MT unit 14, the IVIT unit 14 satisfying below are performed. the prefetch/postwrite start condition may be First, at a step 89, whether or not the fol- 130 sought.

7 GB2192078A 7 The step 71 seeks the MT unit 14 meeting degradation of performance attributed to in the prefetch/postwrite start condition and exe- crease in the start time intervals of IVIT units cutes the prefetch/postwrite schedule process. can be prevented substantially perfectly, and a The details of these operations are illustrated performance equivalent to that of conventional in Fig. 9. 70 magnetic tape devices capable of high-speed At a step 100 in Fig. 9, the IVIT managestart process can be attained. Especially in the ment information part at the head of the pre- present invention, the idle time of a data fetch/poswrite schedule queue 500 is taken transfer path is also considered, so that a pre out. Subsequently, at a step 101, whether or fetch/postwrite process of high efficiency can not the aforementioned equation (1) is fulfilled 75 be performed. Besides, even in a case where is checked. In a case where it is fulfilled, the the respective IVIT units exhibit different ac schedule suspension condition flag 52 is cess rates of recurrence, a buffer size of the turned "on" at a step 102, which is followed following or so suffices:

by a step 106.

In a case where the equation (1) is not fu- 80 (total of stop+ repositioning +start process Ifilled at the step 101, whether or not the time intervals)x(MT data transfer rate)x2 transferred data amount 48 exceeds a predet- Although, in the present embodiment, the ermined amount is checked at a step 103. If IVIT units are supposed as input/output units this holds, the control flow proceeds to the as described above, the present invention is step 106. If the above does not hold, the 85 not restricted thereto, but any input/output corresponding IVIT unit 14 does not satisfy units are applicable as long as pre-processes the start condition, and hence-1 the next IVIT required for performing data transfer pro unit 14 of the prefetch/postwrite schedule cesses and post-processes after data transfers queue 500 is selected at a step 104. have constant distributions.

In a case where the IVIT Units up to the IVIT 90 As regards the present invention, various unit 14 lying at the tail of the prefetch/po- aspects of performance are possible, and they stwrite schedule queue 500 have been will be summed up below:

checked (step 105), this process is ended. In an input/output scheduling method In the other case, the control flow returns wherein in a case where, as to input/output to the step 101. 95 units which perform pre-processes of fixed Next, there will be described processing in time interval off-line from a controller before the case where the IVIT unit 14 satisfying the data transfer processes, a plurality of blocks condition has been found out. are prefetched/postwritten between the inpu At the step 106, the MT management infor- t/output units and a buffer disposed within mation part 27 of this IVIT unit 14 is shifted 100 the controller, a schedule process for deter to the head of the prefetch/postwrite schedule mining a prefetch/postwrite data amount and queue 500. Subsequently, a start request is a p ref etch/ postwrite data transfer start time issued to this IVIT unit 14 at a step 107. of one input/output unit is executed at one Subsequently, a step 108. sets the unscheschedule point; duled data amount 45 at the prefetch/po- 105 (1) a next schedule point is set to be ear stwrite data amount 50 and thereafter clears lier by the pre-process time interval than a the former value. time at which a prefetch/postwrite data trans Further, at steps 109 and 110, in a case fer process scheduled at a present schedule where the read/write flag 43 of this IVIT unit point ends, and whether the prefetch/po 14 is the read request and where the data 110 stwrite schedule process of the input/output amount 44 within the buffer is null, the pre- unit scheduled at the present point is exe fetch adjust data amount within the buffer is cuted or that of another input/output unit is null, the prefetch adjust data amount 46 is executed is further determined depending upon added to the prefetch/postwrite data amount an operating situation at the next schedule po 50. 115 int.

Subsequently, in order to set the next sche- (2) In the method of Item (1), in a case dule point, a step 111 starts the timer 25 so where any other input/output unit satisfying a that the timer flag 26 may turn "on" later prefetch/postwrite start condition does not than the present time by a time interval indi- exist when a schedule has been switched at a cated by the following equation (3): 120 last schedule point, the prefetch/postwrite schedule process is not executed until the in (Prefetch/postwrite data amount) put/output unit satisfying the prefetch/po +0, (3) stwrite start condition appears.

(MT data transfer rate) (3) in the method of Item (1), in a case 125 where the prefetch/postwrite schedule pro where 04 denotes an overhead. cess of the input/output unit different from Lastly, at a step 112, the pr.fetch/postwrite the input/output unit scheduled at a last sche schedule flag 34 is turned "on" to end this dule point has been executed at the present process. schedule point, a pre-process start request is According to the above embodiment, the 130 issued to that input/output unit.

8 GB2192078A 8 (4) In the method of Item (1), the prefetch/- set to be earlier by the pre-process time inter postwrite data transfer process of the inpu- val than a time at which a prefetch/postwrite t/output unit scheduled at the present sche- data transfer process scheduled at a present dule point is started with a delay of the pre- schedule point ends, and whether the pre process time interval from the present schefetch/postwrite schedule process of the inpu dule point. t/output unit scheduled at the present point is (5) In the method of Item (1), the prefetch/- executed or that of another input/output unit postwrite schedule data amount of the inpu- is executed is further determined depending t/output unit at the present schedule point is upon an operating situation at the next sche- set at a data amount taken with reference to 75 dule point. The invention therefore achieves an amount of data transferred between the the remarkable effect that an input/output input/output unit and a channel since the near- scheduling method can be realized by which, est schedule point to the present schedule po- even when the access rates of recurrence of int among schedule points at which the pre- the respective input/output units are not uni fetch/postwrite schedule process of this inpu- 80 form, a data transfer path laid between the t/output unit has been executed. input/output units and the controller for con (6) In the method of Item (1), one of pre- trolling them can be efficiently used, and fetch/postwrite start condition is such that an which can actualize the prefetch/postwrite of amount of data which the pertinent input/out- data with the minimum buffer size.

put unit has transferred between it and a 85

Claims (7)

1. channel since the nearest schedule point to CLAIMS the present point among

   schedule points at 1. In an input/output scheduling method which this input/output unit has been sche- wherein in a case where, as to input/output duled exceeds a fixed value. units which perform pre-processes of fixed (7) In the method of Item (1), one of pre- 90 time interval off-line from a controller before fetch/postwrite start condition is taken with data transfer processes, a plurality of blocks reference to the equation (1) mentioned be- are prefetched/postwritten between the inpu fore, in relation to the pertinent input/output t/output units and a buffer disposed within unit. the controller, a schedule process for deter (8) In the method of Item (1), in a case 95 mining a prefetch/postwrite data amount and where an. amount of data transferred between a prefetch/postwrite data transfer start time the input/output unit and a channel since a of one input/output unit is executed at one - last schedule point till the present schedule schedule point; an input/output scheduling point is null,-the prefetch/postwrite schedule method characterized by comprising the step process of this input/output unit is suspended, 100 of setting a next schedule point to be earlier and a process for searching for any other in- by the pre-process time interval than a time at put/output unit satisfying a prefetch/postwrite which a prefetch/postwrite data transfer pro start condition is initiated. cess scheduled at a present schedule point (9) In the method of Item (1), when the ends, and the step of further determining input/output unit to be scheduled satisfies the 105 whether the prefetch/postwrite schedule pro condition indicated by the aforementioned cess of the input/output unit scheduled at the equation (1), at the present schedule point, present point is executed or that of another the prefetch/postwrite schedule process of input/output unit is executed, depending upon this input/output unit is suspended and any an operating situation at the next schedule po other input/output unit satisfying the pre- 110 int.

   fetch/postwrite start condition is searched for
2. 2. An input/output scheduling method as at the next schedule point. defined in Claim 1, wherein in a case where (10) The prefetch/postwrite schedule data the prefetch/postwrite schedule process of amount in Item (5) is adjusted according to a the input/output unit different from the inpu prefetch data amount within the buffer, of the 115 t/output unit subjected to a prefetch/postwrite input/output unit which is performing a read schedule at a last schedule point has been process. executed at the present schedule point, a pre As described above, according to the pre- process start request is issued to that inpu sent invention, in an input/output scheduling t/output unit.

   method wherein in a case where, as o input/ 120
3. 3. An input/output scheduling method as output units which perform pre-processes of defined in Claim, wherein the prefetch/po fixed time interval off-line from a controller be- stwrite data transfer process of the input/out fore data transfer processes, a plurality of put unit scheduled at the present schedule po blocks are prefetched/postwritten between the int is started with a delay of the pre-process input/output units and a buffer,- disposed 125 time interval from the present schedule point.

   within the controller, a schedule process for
4. 4. An input/output scheduling method as determining a prefetch/postwrite data amount defined in Claim 1, wherein the prefetch/po and a prefetch/postwrite data transfer start stwrite schedule data amount of the input/out time of one input/output unit is executed at put unit at the present schedule point is set at one schedule point; a next schedule point is 130 a data amount taken with reference to an 9. GB2192078A 9 amount of data transferred between the input/output unit and a channel since the nearest schedule point to the present schedule point among schedule points at which the pre- fetch/postwrite schedule process of said input/output unit has been executed.
5. 5. An input/output scheduling method as defined in Claim 1, wherein one of prefetch/postwrite start conditions is such that an amount of data which the pertinent input/output unit has transferred between it and a channel since the nearest schedule point to the present point among schedule points at which said input /output unit has been sche- duled exceeds a fixed value.
6. 6. An input/output scheduling method as defined in Claim 1, wherein letting a prefetch/postwrite start condition be Condition 1, when a condition other than Condition 1 has held and the prefetch/postwrite schedule process of a certain one of the input/output units has been started, the prefetch/postwrite input/output schedule process of sai d input/output unit is continued until Condition 1 holds.
7. 7. As input/output scheduling method substantially as hereinbefore described with reference to the accompanying drawings.

   Printed for Her Majesty's Stationery Office by Burgess & Son (Abingdon) Ltd, Dd 8991685, 1987. Published at The Patent Office, 25 Southampton Buildings, London, WC2A 1 AY, from which copies may be obtained.