Method and system for reporting disk utilisations for disk subsystems

Abstract: The present invention provides a method and system for reporting disk utilisation in a computer system (200). The method includes collecting at least one parameter pertaining to a disk array (206) in a disk subsystem (202) by a processor (210) in the disk subsystem (202); transferring the at least one parameter from the processor (210) to an open system host (204); and calculating disk utilisation based upon the at least one parameter. The method and system is able to provide disk utilisation which is understandable to the open system host (204). In a preferred embodiment, the disk utilisation is provided by collecting the relevant parameters from the microcode in the processor (210) of the disk subsystem (202), and then calculating the average disk utilisation per disk based upon the parameters. Thus, an open system host (204) is able to obtain a useful characteristic for determining the performance of the disk subsystem.

Description: The present invention relates to computer systems, and more specifically to disk subsystems in computer systems. It has been well known in the art with mainframe single disk subsystems to obtain statistics and other characteristics of the mainframe disk subsystem. Examples of disk characteristics of interest include a table of ownership, the amount of disk space used and performance characteristics. An important performance characteristic is disk utilisation. However, a problem arises when with open system hosts a disk subsystem including a disk array attempts to communicate with the host, such as hosts which run UNIX, Windows NT, or some other type of open operating system. In such an open systems environment, the open system host is unable to obtain the actual disk utilisation characteristic. The article "Sibling PEND: like a wheel within a wheel" by H. P. Artis in CMG Proceedings v 1 1996. CMG, Westmont, IL, USA discusses disk utilisation measurement problems on multiple disk array storage systems. Accordingly, there exists a need for a method and system for providing parameters for a disk subsystem to an open system host to enable determination of actual disk utilisation. The method and system should be able to provide disk utilisation characteristics which are understandable to the open system host. The present invention seeks to address such a need. According to one aspect of the present invention, a method is provided for reporting disk utilisation in a computer system utilising a RAID array in a disk subsystem, the method comprising the steps of: (a) collecting, by a processor in the disk subsystem, as disk array parameters, for a time interval in seconds (T) and number of disks in the RAID array (N); the milliseconds of read time (MR) in the time interval (T); the milliseconds of write time (MW) in the time interval (T); the total number of writes (W) in the time interval (T); and the number of stride write destages (S) in the time interval (T); (b) transferring these parameters from the processor to an open system host; and (c) calculating disk utilisation (U) with these parameters employing a formula U=1/(1000*T*N) * (MR + (MW/2W-S) * (4*(W-S) + N*S)). According to a second aspect of the present invention there is provided, a computer system comprising: a disk subsystem having a RAID array and a processor coupled to the disk array, the processor being capable of collecting as disk array parameters, for a time interval in seconds (T) and number of disks in the RAID array (N), the milliseconds of read time in the time interval (MR), the milliseconds of write time in the time interval (MW), the total number of writes in the time interval (W), and the number of stride write destages in the time interval (S); and an open system host coupled to the disk subsystem, the open system host being capable of receiving these parameters from the processor and of calculating a disk utilisation (U) based upon the parameters, employing a formula U=1/(1000*T*N) * (MR + (MW/2W-S) * (4*(W-S) + N*S)). According to a third aspect of the present invention, a computer readable medium is provided with computer instructions for reporting disk utilisation in a computer system, the instructions being for: (a) collecting, by a processor in the disk subsystem, as disk array parameters, for a time interval in seconds (T) and number of disks in the RAID array (N); the milliseconds of read time (MR) in the time interval (T); the milliseconds of write time (MW) in the time interval (T); the total number of writes (W) in the time interval (T); and the number of stride write destages (S) in the time interval (T); (b) transferring these parameters from the processor to an open system host; and (c) calculating disk utilisation (U) with these parameters, employing a formula U=1/(1000*T*N) * (MR + (MW/2W-S) * (4*(W-S) + N*S)). For a better understanding of the present invention reference will now be made to the accompanying drawings, in which, by way of example: Figure 1 illustrates a preferred embodiment of a computer system with a disk subsystem in accordance with the present invention; Figure 2 is a flow chart illustrating a preferred embodiment of reporting disk utilisation in accordance with the present invention; and Figure 3 is a flow chart illustrating in more detail the reporting of disk utilisation in accordance with the present invention. The present invention provides a method and system for providing parameters for a disk subsystem to an open system host. The following description is presented to enable one of ordinary skill in the art to make and use the invention and is provided in the context of a patent application and its requirements. Various modifications to the preferred embodiment will be readily apparent to those skilled in the art and the generic principles herein may be applied to other embodiments. Thus, the present invention is not intended to be limited to the embodiment shown but is to be accorded the widest scope of the appended claims consistent with the principles and features described herein. Figure 1 of the drawings shows a computer system 200, which comprises a disk subsystem 202 and an open system host 204. The disk subsystem 202 comprises a disk array 206, a cache 208, and a processor 210 which controls the functioning of the disk subsystem 202. The open system host 204 communicates with the disk subsystem 202 by interfacing with the processor 210 via an Internet connection. Software resides in the processor 210 and the open system host 204 to facilitate this communication; the processor 210 comprises the specialist software 212, and the open system host 204 comprises the expert software 214. Clearly, software functions may be reproduced by hardware configurations and throughout the specification the terms "specialist" and "expert" used alone are intended to cover either software or hardware capable of performing the required functions. One of the functions of the specialist 212 is to gather certain parameters from the microcode (not shown) within the processor 210 which pertain to disk characteristics and transfers them to the expert 214 in the open system host 204. One of the functions of the expert 214 is to receive the parameters from the specialist 212 and to generate reports concerning disk characteristics based upon the parameters. The reports may be in tabular or graphical form. For the computer system 200, microcode within the processor 210 does not provide disk utilisation directly. Thus, the expert 214 comprises a software routine 216 which calculates disk utilisation from the parameters provided by the microcode via the specialist 212. An example of a disk subsystem which may be used in the computer system 200 is the ENTERPRISE STORAGE SERVER (ESS) disk subsystem developed by INTERNATIONAL BUSINESS MACHINES CORPORATION. In the ESS disk subsystem, the disk array 206 is a RAID array, which is well known in the art. Figure 2 is a flow chart illustrating a preferred embodiment of reporting disk utilisation in accordance with the present invention. First, the specialist 212 in the processor 210 of the disk subsystem 202 collects the parameters, via step 302. Next, the parameters are transferred from the specialist 212 to the expert 214 in the open system host 204, via step 304. Then, the expert 214 calculates the disk utilisation from the parameters, via step 306. In the preferred embodiment, the calculation is performed with a disk utilisation routine 216 in the expert 214. The disk utilisation, along with other disk characteristics, may be displayed by the expert 214 in the form of a report. Figure 3 is a flow chart illustrating in more detail the reporting of disk utilisation in accordance with the present invention. First, once the user logs into the open system host 204, the user requests disk characteristics for the disk subsystem 202, via step 402. This request may be in the form of a schedule. For example, the user may request that certain disk characteristics be collected from the disk subsystem 202 every 10 minutes, or every hour. One of the disk characteristics which may be requested by the user is disk utilisation. Next, the expert 214 sends a request to the specialist 212 for the disk characteristics, via step 404. When the user requests disk utilisation, the expert 214 requests that the parameters in the microcode which are relevant to disk utilisation be collected. For a computer system 200 which uses the ESS disk subsystem, the relevant microcode parameters comprise the following: T = time interval in seconds N = number of disks in a RAID array MR = milliseconds of read time in the time interval MW = milliseconds of write time in the time interval W = total number of writes in the time interval S = number of stride write destages in the time interval The specialist 212 then collects the parameters from the microcode according to the request, via step 406. Next, the specialist 212 transfers the parameters to the expert 214, via step 408. Thus if the user requests that disk characteristics be collected every 10 minutes, then at 10 minute intervals, the parameters would be collected from the microcode and sent to the expert 214. Each time the expert 214 receives the parameters, they are stored in a database (not shown) on the open system host 204, via step 410. When the user is ready to view the disk characteristics, the user requests a report from the expert 214, via step 412. The expert 214 then calculates disk utilisation for each disk in the array 206 from the parameters stored in the database, via step 414, using the disk utilisation routine 216. For a computer system 200 which uses an ESS disk subsystem, the formula for the average disk utilisation per disk is as follows: U = 1/(1000*T*N) * [MR + (MW/2W-S) * (4*(W-S) + N*S)] The formula is derived based upon the fields which are provided by the microcode and their meaning, and an understanding of the internal working of the hardware of the disk subsystem 202. For example, the formula takes into account how a read, write, and stride write destages are performed by the disk subsystem 202, and how the cache 208 and the disk array 206 are involved. For this formula, U is a number between 0 and 1. Once calculated, the expert 214 then displays the report, which includes disk utilisation, via step 416. The report may be in a tabular or graphical form. Disk utilisation for each disk in the array 206 may be displayed as a percentage, representing the amount of time a disk is in use during the interval of time, T. The parameters of the microcode described above is part of a proposed standard currently before the Storage Network Industry Association (SNIA). If the parameters are adopted as the standard, then the method and system of the present invention may be used to conform disk utilisation reporting to this standard. A method and system for providing parameters for a disk subsystem to an open system host has been disclosed. The method and system is able to provide disk utilisation which is understandable to the open system host. The disk utilisation is provided by collecting the relevant parameters from the microcode in the processor of the disk subsystem, and then calculating the average disk utilisation per disk based upon the parameters. Thus, an open system host is able to obtain a useful characteristic for determining the performance of the disk subsystem. Although the present invention has been described in accordance with the embodiments shown, one of ordinary skill in the art will readily recognise that there could be variations to the embodiments and those variations would be within the scope of the appended claims.

Claims: A method for reporting disk utilisation in a computer system utilising a RAID array in a disk subsystem, the method comprising the steps of: (a) collecting, by a processor in the disk subsystem, as disk array parameters, for a time interval in seconds (T) and number of disks in the RAID array (N); the milliseconds of read time (MR) in the time interval (T); the milliseconds of write time (MW) in the time interval (T); the total number of writes (W) in the time interval (T); and the number of stride write destages (S) in the time interval (T); (b) transferring these parameters from the processor to an open system host; and (c) calculating disk utilisation (U) with these parameters employing a formula U=1/(1000*T*N) * (MR + (MW/2W-S) * (4*(W-S) + N*S)). A computer system, comprising: a disk subsystem, having a RAID array, and a processor coupled to the disk array, the processor being capable of collecting as disk array parameters, for a time interval in seconds (T) and number of disks in the RAID array (N), the milliseconds of read time in the time interval (MR), the milliseconds of write time in the time interval (MW), the total number of writes in the time interval (W), and the number of stride write destages in the time interval (S); and an open system host coupled to the disk subsystem, the open system host being capable of receiving these parameters from the processor and of calculating a disk utilisation (U) based upon the parameters, employing a formula U=1/(1000*T*N) * (MR + (MW/2W-S) * (4*(W-S) + N*S)). A computer readable medium provided with computer instructions for reporting disk utilisation in a computer system having a disk subsystem with a disk array, the instructions being for: (a) collecting, by a processor in the disk subsystem, as disk array parameters, for a time interval in seconds (T) and number of disks in the RAID array (N); the milliseconds of read time (MR) in the time interval (T); the milliseconds of write time (MW) in the time interval (T); the total number of writes (W) in the time interval (T); and the number of stride write destages (S) in the time interval (T); (b) transferring these parameters from the processor to an open system host; and (c) calculating disk utilisation (U) with these parameters, employing a formula U=1/(1000*T*N) * (MR + (MW/2W-S) * (4*(W-S) + N*S)).

Inventors: AZEVEDO RUTH ENID, GOODGOLD STUART R, MCNUTT BRUCE, AZEVEDO, RUTH ENID, GOODGOLD, STUART R., MCNUTT, BRUCE, Azevedo, Ruth Enid, IBM UK Ltd., I.P.L., Goodgold, Stuart R., IBM UK Ltd., I.P.L., McNutt, Bruce, IBM UK Ltd., I.P.L.
Applicants: IBM, INTERNATIONAL BUSINESS MACHINES CORPORATION
Application year: 2000
Main classification: G06F3
IPC codes: G06F3, G06F11, G06F9