GB2184267A - File allocation - Google Patents

Abstract

A method for optimum allocation of files to storage devices is disclosed in which in order to realize a desired hit ratio, number of writes, and read/write ratio within suitable ranges and to reduce the number of steps for file allocation judgement, the actual hit ratio for the cache of each of the files stored in storage devices with cache and the read/write ratio are measured and calculated and whether they are greater than values specified respectively therefor or not is judged. Further, when using an integrated circuit external storage device, the number of accesses to it is measured, and whether the number thus obtained is smaller than a specified value or not is judged. Files are reallocated on the basis of the judgement, the storage capacity of the devices, and allowable utilisation rates of the devices. <IMAGE>

Description

SPECIFICATION File allocation method and apparatus therefor Background of the invention This invention relatesto a file allocation method and an apparatus therefor, and in particularto a method for allocating software resources such as files, programs, etc. (hereinbelow they are generally called files) in a computer system provided with a plurality of storage devices including storage devices with cache or integrated circuit storage devices and a file allocation apparatus for realizing this method.

It is thought that magnetic disks with integrated circuit external storage devices or semiconductor buffers (cache) will be important external storage devices in the future. Heretofore, how to allocate a group of files a group of external storage devices is an importantfactorfor performance and reliability of a whole computer system, but this allocation work has been difficult and required too many steps. Introduction ofintegrated circuit external storage devices (semiconductor disks) or disks with cache described above increasesfurther this tendence.

In the determination in allocation of the files to selected storage devices, if for example, those files used often are allocated to one device, load will be concentrated to this device and there is a fearthatthis device gives rise to a narrow path in the performance. Further, if those files indispensablefora specificworkare allocated to one device, any trouble, when occurred in this device, will undesirably affect the work greatly.

This isthefirst problem.

Further, the following can be pointed out as the second problem expected when new recording mediums appear.

Heretofore many magnetic recording mediums (disk, drum, floppy disk, bubble, tape, etc.) have been used as recording medium. These have advantages that it is easy to update stored content and furtherthatthe stored content is kept almost permanently. On the other hand, since they need mechanical parts; they have a disadvantage that the access time is aptto be too long. On the other hand, recently, storage devices provided with integrated circuit external memory devices (IC disks) or semiconductor buffers (caches) are introduced.

However, those semiconductor devices used forthis purpose are generally ofthevolatiletype dueto economic reasons. In this case, there is a fearthatstored contents disappearwhen the power sourceforthe semiconductor devices is interrupted. In addition, many processing steps are necessaryforobtaining journals (log) of update request (processing request accompanying update of stored content), recovering stored content, in the case where power source for the semiconductor devices is interrupted, etc. Therefore it is disadvantageous to dispose files updated frequently.

Furthermore, in the case where storage medium with cache is used, the reference request (request onlyfor referring to stored content, which is not accompanied by rewrite), is responded such that when a desired file is present in the cache (called hit), this file is read and writen in the main storage device, while when it is not present, it is read out from the memory medium and sent to the main storage device. On the other hand, the update request is responded such that even if the desired file is present in the cache, boththefile in the cache and the file in the storage medium (e.g. disk) should be updated and the number of processing steps rather increases. Forthis reason, it is advantageous to dispose those files, whose update frequency is high, in a storage medium with cache.Consequently, the performance and reliability of a computer system using IC disks, storage mediums with cache, etc. are remarkably influenced by the ratio (called readlwrite ratio) ofthe numberofaccesses (the number of reads) due to reference request for every file provided therein to the number of accesses (the numberofwrites) due to update request and the hit ratioforthe cache.

In order to deal with these problematical points described above,thefollowing two methods would be considered in a computer system provided with a plurality of storage devices. In the first method, the number of accesses to the storage device for utilization of each ofthe files prepared for respective different kinds of processing requests is measured, and the measured values of the access times are utilized to find (i) a condition which minimizesthetotal time necessary for utilization of the storage devices under restriction of the allowable storage amount and allowable utilization of each ofthe storage devices; and/or (ii) a condition which fulfils availability contraints for each ofthe different kinds of processing requests; andíor (iii) a condition which suppresses the extent of influences under an allowable value in the case where a trouble is produced in a partofthe storage devices, wherebythefiles are allocated to the suitable storage devices soas to satisfy a selected combination of the conditions (i) to (iii) described above. However, bythis method, in the case where IC disks orstorage devices with cache are contained, since the hit ratio and the read/write ratiofor each file are not taken into consideration for allocating thefiles, the second problem as mentioned above cannot be solved.

The second method is considered to solve the second problem. That is, in the second method, whetherthe hit ratio orthe read/write ratio of each file and the number of writes of each file contained in the IC disks are within predetermined restriction conditions is judged and indicated to the operator.

However, since the rearrangement of files on the basis of the above indication exclusively relies on judgement of the operator, a large number of steps are requiredforthejudgementand it is not possibleto fulfil satisfactorily requirements for performance, reliability and economy.

Summarv ofthe invention The object of the invention is to solve the problems described above of the prior art and to provide a method and a device for allocating files to storage devices, by which it is possible to realize a hit ratio,a number of writes and a read/write ratio, of suitable values and to reduce the number of steps in for judgement offile allocation.

In orderto achieve this object, in one aspect ofthe present invention, the method for allocating files to storage devices is arranged such that the hit ratio forthe cache of each ofthefiles stored in the storage devices with cache and the ratio of the number of accesses in reference requests to that in update requests are measured and calculated; whetherthe hit ratio and the ratio of the numbers of accesses are greaterthan values specified respectively therefor or not is judged; and in the case where it is judged that the former is not greaterthan the latter, it may be indicated to the operator.

In another aspect of the invention, when an integrated circuit external storage device is provided the number of accesses to the storage device due to update requestfor each file stored in the storage device is measured; whetherthe measured numberofaccesses is smallerthan a specified value or not is judged; and in the case where itisjudgedthattheformer is notsmallerthanthe latter, it may be indicated to the operator.

Briefdescription ofthe drawings Figure lisa block diagram illustrating a file allocation device, which is thefirstembodiment ofthis invention.

Figure2 is a flow chart for explaining the working mode of the file arrangement and calculation device in Figure 1.

Figure 3 is a block diagram illustrating a file allocation device, which is the second embodiment ofthis invention.

Description ofthepreferred embodiments Hereinbelow, some embodiments ofthis invention will be explained, referring to the drawings.

Figure lisa block diagram illustrating a file allocation device, which isthefirst embodiments ofthis invention.

In Figure 1, reference numerals 1(1)-i (K) representstorage devices (only 1 (k) and 1 (K) are indicated in thefigure). IC desks, storage devices with cache, storage devices without cache can be used as medium. Each of files is sotred in any one of the storage devices. 2(1) - 2(L) indicate controllers for the storage devices provided with cache mechanism (hereinbelow called cache devices). A control device 3 for controlling file utilization stores information of statistics on the utilization situation of each file which is updated every time interval AT previously specified.

3 (j, 0), 3 (j, 1 ),-----,3(j,5)[(j=1 ---J)] represent registers memorizing the storage amount qj of the file j,the number of reference type accesses (number of reads) necessary for utilization of the file j at #T,similarly the number of update type accesses (number of writes), the hit ratio, the access rate represented by the number of accesses per unit storage amount (i.e. (number of reads + number of writes)/qj) and the order in magnitude ofthe access rateofthefile, respectively.

4 4 is a control device for controlling utilization ofthe device, which stores a utilization rate of each ofthe storage devices 1(1) - 1(K) and the cache devices 2(1) - 2(L) detected at the last time interval ##. The registers 4.1 (k) [ k= 1 --K] 4,2 (#)[# = 1--- Li store utilization rate of the storage devices 1(1)-i (K) and that of the cache devices 2(1 )-2 (L), respectively. 5 is a file arrangement decision device, which includes afile arrangement and calculation device 6, afile rearrangement pattern control device 8, a control device 9 for controlling various parameters ofthe storage devices and a control device 1 0 for controlling various parameters of the cache devices:Registers 8 (k, j) [k = 1---K, j = 1,---J] in the file rearrangement pattern control device store "1", ifthefilej should be again arranged in the storage device k, and "0", if not. Registers 9 (k, 1 ) --- 9 (k,8) [ k=1--- K] in the storage device-parameter control device 9 store identification forthe storage type of the storage device k (magnetic disk, IC disle magnetic tape, etc) [9 (k, 1 )1, the identification numberofa cache device which is connected thereto (in the case where there is no cache, the identification symbol indicating no cache) [9 (k, 2)1, the necessary time per access [9 (k, 3)1, the allowable utilization rate [9 (k, 4) ] ,the storage capacity [ 9 (k, 5)1 and the allowable number ofwrites in the case ofthe IC disk [ 9 (k, 5')j, respectively, and 9 (k, 6), 9 (k,7), 9 (k, 8) are all work areas. 10(#, 1)---10(#, 5)[# = 1--- k] in the cache device-parameter control device 10 store the necessary time per access, when hit, at a reference request [ 10 (,', 1)], the necessary time per access, when miss, hitata reference request [ 10 (, 2)1 and the necessary time peraccess forthe update request [10 (, 3) ] . Further 10 (e, 4) indicates a work area and 10 (f, 5) is a registerstoringthe allowable utilization rate. 11 is a control device for controlling the present file arrangement pattern.Registers 11 (k,j) [ k=1 --- K,j=1 ---J ] store "1", if the file j is arranged in the storing device k atthattime, and "0", if not.

"1" and "0" are called presentfile arrangement patterns. 12 is a file rearrangement execution device, which compares the optimum file arrangement pattern determined by the file arrangement decision device 5 and a calculation result correction device 15 with the present file arrangement pattern coming from a present file arrangement pattern control device 11 and effects modifications ofthe file arrangement so as to cause the formerto coincide with the latter. 13 indicates a calculation condition input device; 14 afilearrangement calculation result indication device; and 1 5 a calculation result correction device for indicating modifications ofthe file arrangement.

Next the outline of the work of the file allocation device indicated in Figure 1 will be described.

At first, the operator (the user of the computer system) effects initial input or corrections of various parameters in the control device 9 for controlling various parameters of the storage devices by using the calculation condition input device 13.

The file arrangement decision device 5 is started (i) when it receives an indication from the input device 13 by the operator, or (il) when the utilization rate of any one of a storage device kin the registers 4.1 (k) [ k= 1 -- K] and a cache device 4 in the registers 4.2 () [ 4=1 --- L] exceeds its allowable utilization rate, i.e. "k" indicated in the register9 (k, 4) or "4" indicated in the register 10 (4, 5), or (iii) periodically.

Figure 2 shows a flow chart illustrating the working mode of the file arrangement and calculation device indicated in Figure 1. The operation of the file arrangement and calculation device is based on a principlethat thefiles are allotted, successively in order of magnitude of the access rate: i.e. access frequency per storage capacity fron a higher one, to one of the stotage devices which has a higher processing speed so long as the utilization rate and storage capacity of that storage device are kept within limits and the utilization rate of its cache device and the number of writes of each file in the IC disk, if used, are kept within limits.In addition, in the case of the storage devices with cache, it should be taken into account that the processing speed varies depending on whetherthe process is for responding to reference request or update request and further whether, in case of the reference request, the file is hit or mis-hit.

In Figure 2, atfirst,thefile rearrangement pattern registers8 (k, j) [ k--1 --- K,j=1 ---J], the work areas 9 (k,6) 9 (k,7), 9 (k, 8) [k = 1---K] for the storage amount Qk, the utilization rate Pk and the integration of writes Wk of a storage device k,andtheworkareasl0(("'1--- --- forthe utilization rate Pe of a cache device 4 are all setto zero (Step). Calculate the following formula for all of j= 1 --- J and write the numbers thus obtained into the register3 (j,5) in order of magnitude thereof from the largest (Step);; A = (Rj + Wj)/qj --------- (1 ) Now, the files are renumbered asj0--1, in in orderofthe magnitude of Athus obtained from the largest.

Starting from j0=1, effect the following processing for every j (Step). Set the access time Tjo to the file j in its optimum storage device at a predetermined very large value (Step 4). Effect the following processing for every storage device k (Step 5). Read already allocated amounts Qk and the allowable storage capacity Qk* of the device kfrom the resisters 9 (k, 6), 9k, 5) and the storage capacity qjo of the file j0 from the register 3 (j , 0).

The, examine whether the following formula is valid or not; Qk + qj > Okn Goto Step, ifit is not valid and to StepQ3, if it is valid. Examine the identification symbol f: (k) ofthe cache device with which the device k is connected from the content ofthe register9 (k, 2) and proceed to Step Qo. However, if it is not connected, examine the type of the storage device from the resister 9 (k, 1 ) and proceed to Step 8, if the type is lc disk and to Step 9, if not IC disk (Step 7. Examine the number Wf of writes of the file j from the contents ofthe register3 (j , 2).After that, examine whetherthe sum of Wf and Wkwhich is the accumulated value of writes of the storage device kstored in the register 9 (k, 8) exceeds the allowable value Wk* stored in the register 9 (k, 5') (Wk + Wf > Wk*) or not. Proceed to Step 13, if the former exceeds the latter, and to Step 9, if not (Step 8). Read the number Rjo of reads and the number Wjo of writes from the registers 3 (j , 1 ) and 3 (j , 2), respectively, and the access time tk and the allowable utilization rate Pk* ofthe device k from the registers 9 (k, 3) and 9 (k, 4), respectively, and judge the following formula; Pk + (Rjo + Wjo) tk > Pk* ----------- (3) If aboveformula is valid, proceed to Step 0 and ifnot, effectthe succeeding judgement.That is, reads tk from the register 9 (k, 3) and if the following formula (4) is valid, set k to k and proceed to Step 13. If it is not valid, proceed to Step Q3 (Steps, 9', 9").

to two (4) Read Rjo, Wjo and the hit ratio hio of the file j from the resisters 3(j , 1), 3 (j , 2) and 3 (j , 3), respectively, and read tk, Pk* of the device k from the resisters 9 (k, 3) and 9 (k, 4), respectively. Thereafter, effectthefollowing judgement; Pk + APk > Pk, ----------( (5) where #Pk = [Rio # (1 - hio) + Wio]tk.

Proceed to Step, if the above formula (5) is valid, and to Step O, if not (Step 10) 0) l Read the access time t,Rk) ata reference request when hit, the accesstimet,RM (k) at a reference request when mis hit and the access time tW(k) atan update request, and effectthefollowing judgement; P#(k) + #P#(k) > P#(k*),------- (6) where AP 1k) = Rjo.hjo.t & +R1o.( 1 hjo).t1R +Wjo.tWk).

Proceed to Step13, if the above formula (6) is valid, and to Step if not (Step Qi). In Step 12 effect the judgementofvalidity ofthefollowing formula;

The left member of the above formula (7) indicates the mean value of the access time of the storage device kwith cache with respectto the file j . If the formula (7) is valid, substitute k by k and proceed to Step 13 (Step 9 "). If not, proceed to Step 9 (Step &commat; ). In Step 13, judge whether the following formula is valid or not.

k'K -----------------(8) (8) If the above formula (8) is notvalid, increase the value of k by 1 and return to Step. If it is valid proceed to Step 14 (Step 13).

If a device k is found, i.e. the process reaches the step' after executing the Steps to ' or6X, proceed to Step 15: If not found, it is indicated on the display device 14 that the arrangement of the filr j is impossible and terminate the operation (Step 8 )- In Step (, set"1 " at the register 8 (k , j ) and add qjo to the work area 9 (k, 6) for operation (OkO + qjo). In step 16, examine the identification symbol C (k ) of the cache device, with which k is connected, by using 9 (k , 2) and proceed to Step 19. Then, examine the type of the storing device by usig the register 9 (k , 1).

Proceed to Step 17, ifthetype is IC disk, and to Step 18, if not. If step), add who (stored in 3 (j0, 2)) tOWkO in the register 9 (k , 8). In Step add APkoto the register9 (k , 7) and proceed to&commat;. Here #Pko = (RjO + Wio)tko is valid. In Step , add Ako to the register 9 (k , 7) and APe (k ) to the register 10(# (k ), 4) and proceed to Step &commat;, where

in Step 20 effect a judgement by using the following formula (9). If it is valid, terminate theoperation of he file arrangement and calculation device 6, and if it is not valid, add 1 to j , return to Step 4; and repeat again the same operation.

j #J ---------- (9) The file arrangement and calculation device 6works, as indicated above. As the result, "1 " is inscribed at the place corresponding to the files, which are to be allocated to the storage devices, respectively, inthe registers 8 (k, j) [k = 1--- K,j=1 ---J] of the file rearrangement and calculation device. Thefilearrangement decision device 5 outputs this content and othercalculation results to the display device 14. The operator sees this output content and inputs if necessary a correction data through a calculation result correction device 15. In the case where the operator judges that it is unnecessary to correctthe present arrangement, he inputs identification information representing thatjudgementthrough the correction device 15.The correction device 1 5 transmits the inputted information to a control device 8 forcontrolling file arrangement and modified items. If some corrections are specified, the control device 8 rewrites the relevant places in the registers 8(k,j) [ k=1--- K,j=1 ---J ] on the basis ofthetransmitted information.

Next, the file rearrangement and execution device 12 compares the registers 8 (k, j) [k = 1--- K,j=1 ---J ] with the registers 11(k,j) [ k--1-- K,j=1 --- J] in the control device 11 for controlling present file arrangement pattern and modifiesthefile arrangementto the storage devices so asto cause the latterto coincidewiththe former. Afterthat, the file rearrangement and execution device 12 substitutes the contents of the registers 11 (k, j) bythose ofthe registers 8 (k, j), where k= 1 --- K,j=1 ---J.

In addition, although this invention has been realized by disposing newly afile arrangement decision device Sin Figure 1, it is possibleto realize this new device 5 entirely with software. Forthe devices otherthan the file arrangement decision device 5, devices disposed in a usual computer system may be used.

Inthisway, in the first embodiment is disposed a file arrangement and calculation device 6, which presupposes the number of writes to each of the IC disks; judges wheter this value fulfils restriction conditions previously specified; moreoverforthe case of storage devices with cache calculates the utilization rate of each ofthe memory devices, taking the read/write ratio and the hit ratio into account; calculatesthe allocation ofthe files to the storage devices periodically or every time when the utilization status ofthefiles fails to satisfy the specified restrictive conditions; and executes the re-allocation of the files to the storage devices on the basis of the results thus obtained.

Consequently, according to this invention, in a computer system provided with a plurality of storage devices including storage devices with cache or IC disks, the files are allocated to the storage devices so asto minimize the total time and the total cost necessaryfor utilization ofthe storage devices, while the restrictive conditions in the numberofwrites of each IC disk, the allowable storage capacity and the allowable utilization rate of each of the storage devices including those with eache, and the allowable utilization rate of each ofthe cache devices are satisfied.Therefore, even for storage devices with cache and those including IC disks, itis possibleto increase the utilization rate in while ofthe storage devices, to decrease the cost ofthestorage devices, to increase the reliability with respectto the interruption of the power source for IC disks, and also to reduce the numberofjudgementsteps necessaryforthe allocation ofthefiles to the storage devices.

Figure 3 is a block diagram illustrating afile allocation devices, which is the second embodiment ofthis invention.

In Figure 3, what is different from the device illustrated in Figure 1 is that the control 4forcontrolling utilization of the device and the control device 10 for controlling various parameters of the cache devices in the file arrangement decision device 5 are removed. Since the construction of the other parts is completely identical to that shown in Figure 1, explanations therefor will be omitted.

The file arrangement and calculation device 6 in Figure 3 effects calculations for judgement whether a given file arrangement pattern fulfils previously specified restrictive conditions in the number of writes, the read/write ratio and the hit ratio or not, in a way similarto that in the device in Figure 1.

At first, the operator startsthefile arrangement decision device 5 by using the calculation condition device 13 and at the same time inputs the upper limit of the write frequency (the number of update access times per unittime)forthe IC disk k,the lower limitofk* ofthe read/write ratio forthe storage device with cache kand the lowerlimithk* ofthe hit ratio. Wk*, ak* and hk* stated above are numerical values to be decided empirically or on the basis of scientific experimental results.In this way, atfirst, the file arrangement decision device Stransmitsthe contentofthe register 11 (j, k) in the control device 11 for controlling presentfile arrangement pattern to the register8 (j, k) in the control device 11 for controlling file arrangement and modified items 8, where j=1 --- J, k= 1 ---K. Next, the file arrangement and calculation device 6 proceeds to the processing shown in Figure 2. The calculation device 6 examines the registers 9(k, 1), 9(k, 2) [ k=1 --- K ] inthe control device 9 for controlling various parameters of storage devices, and thus examines identification symbols of the storage devices (k'=1---K'), whose storage devices type is IC disk, or the storage devices (k"= 1 --- K") connected with cache devices.Then, the calculation devices 6 effects the following process for each of the storage devices k'. That is, it examines a group of files, which the device k' contains, by using the control device 11 for controlling the present file arrangement pattern; afterthat, examines the register3 (j, 2) (i.e. the numberofwrites) corresponding to the group offiles (j'=1 ---J') by using the file utilization control device 3; and compares the values thus obtained with the allowable value Wk,*. If the number ofwritesforj' > Wk'*, the pair of [ k', j' ] is stored. Further, here,W'* is the upper limit of updated timesforthe storage device k'. After that, it proceeds further to the following process for each ofthe devices k".That is, it examines a group of files (j"=1 ---J"), which the device k" containes, by using the control device 11 forcontrolling present file arrangement pattern; afterthat, examines the contentofthe corresponding registers 3 (j", 1 ),3 (j", 2), 3 (j", 3), i.e. the number of reads, the number of writes and the hit ratio, for each ofthem by using the file utilization control device 3; and judges whether both of the following formulas arefulfilles or not; NUbOfd5fO,,*,(10) Numberofwritesforj Hitratiofori hk* -------(11) In the case where both the above formulas (10) and (11) cannot be satisfied,that pair [ k",j"j and the not satisfied formulas are stored. The file arrangement and calculation device Gtransmits the resultthus obtained to the calculation result display device 14.The display device 14 indicates an assembly of pairs [ k', j' ] as the files contained in the storage devices, which don't satisfy the restrictive condition in the numberof writesforthe IC disks and an assembly of pairs [ k",j" ] as the files contained in the storage devices, which don't satisfy any one or both ofthe restrictive conditions of the read/write ratio and the hit ratio forthe storage devices with cache. The operator judges a plan of modifications in allocation of the group offilesto the storage devices on the basis ofthe contentofthe display and rewrites the relevant items of the registers8 (j, k) [ j=1 --- J, k= 1 --- K] through the calculation result correction system 15.Next, the file rearrangement execution device 12 compares the register8 (j, kin the file arrangement control device 8 and modified items with the registers 11 (j, k) [ j=1 ---J, k=1 ---K] in the control device 11 forcontrolling presentfile arrangement pattern and modifies the file arrangement to the storage devices so as to cause the arrangement pattern of the formerto coincide with that ofthe latter. Afterthat, the file rearrangement execution device 12 rewrites the content of the register 11 (j, k) to thatofthe register8 (j, k).

In addition, in the second embodiment, although the newly disposed file arrangement decision device 5 is represented with a hard ware, it is possible to realize itentirelywith software. The devices otherthan thefile arrangement decision device Scan be realize by adding existing functions to a usual computersystem.

In this way, in the second embodiment, means for measuring the hit ratio, the number of reads andthe number of writes for each of the files, and meansforjudging, on the basis of information on the measured values, whetherthe hit ratio and the readiwrite ratio for each of the files contained in the storage devices with cache, as well as the number of writes for each of the files contained in the IC disks fulfil previouslyspecified restrictive conditions or not are added to the file arrangement and calculation device, and the resultofthis judgement is indicated to the operator. In this case, since, when the previously specified restriction con ditions are notfulfilled,this is indicated to the operator, this invention permits to utilize the storage devices with cache with a high efficiency, by storing with a high hit ratio and a high read/write ratio therein, and furtherto utilize it with a high reliability and a high efficiency by storing the files, whose number of writes is small, in IC disks.

As explaned above, according to this invention, effects are obtained that it is possibleto realize the hit ratio, the number of writes, the read/write ratio, etc. Within a domain of suitable values and to reducethe number of steps for file allocation judgement.

Claims (9)

1. A methodforallocating files to a group of storage devices, comprising the steps of measuring and calculating the hit ratio forthe cache of each ofthefiles stored in the storage devices with cache andtheratio of the number of accesses of reference request to that of update request; and judging whetherthe hit ratio and the ratio of the numbers of accesses are g reaterthan values specified respectively therefor or not.

2. Amethodforallocating files to a group of storage devices, comprising the steps of measuring,with respect to an integrated circuit external storage device, the number of accesses to said integrated circuit external storage device and judging whetherthe number ofaccessesthus obtained issmallerthan aspecifled value or not.

3. A method according to Claim 1, in which, in the case where the result of the judgement is negative, itis indicated.

4. A method according to Claim 2, in which, in the case where the result of the judgement is negative, itis indicated.

5. An apparatus for allocating files to a group of external storage devices including storage deviceswith cache, said apparatus comprising: first storage meansforstoring a number of reference requests and a number of update requests issued to each ofthefiles as well as a hit ratio to the cache of each ofthefiles; second storage means for storing a processing speed, an allowable utilization rate and an allowable stor ae capacity of each ofthe storage devices, as well as an allowable utilization rate, a numberofhits atthe reference requests, a number of mis-hits at the reference requests and a processing speed for each ofthe update requests for each of cache devices; and meansforallocating the files to the group of storage devices such that total time necessary for accesses to the storage devices is minimized on the basis of information stored in said first and second storage means, while satisfying restrictive conditions in the allowable utilization rate and the allowable storage capacity of each ofthe storage devices as well as the allowable utilization rate of each ofthe cache devices.

6. An apparatusforallocating files to a group of external storage devices including integrated circuit external storage devices, said apparatus comprising: first storage meansforstoring the number of update requests to each ofthefiles;; second storage meansforstoring a processing speed, an allowable utilization rate, an allowable storage capacity and a number of update requests of each of the storage devices, and means for allocating the files to the group of storage devices such that total time necessaryforaccessesto the storage devices is minimized on the basis of information stored in said first and second storage means, while satisfying restrictive conditions in the allowable utilization rate and the allowable storage capacity of each ofthe storage devices as well as the allowable number of update requests to each of said integrated circuit external storage devices.

7. An apparatus for allocating files according to Claim 5,further including integrated circuit external storage devices, and in which said second storage means further stores an allowable numberofupdate requests of each of the storage devices, and allocates the files to the group of storage devices so as to further satisfy a restrictive condition in the allowable numberofupdate requests to each ofsaid integrated circuit external storage devices.

8. An apparatus for allocating files to a group of external storage devices, such apparatus being constructed and arranged to operate substantially as herein described with reference to and as illustrated in the accompanying drawings.

9. A method of allocating files to a group of external storage devices substantially as herein described with reference to the accompanying drawings.