Something I ran into recently as a consideration if you keep growing real storage sizes. Set the Wayback Machine Sherman!
Way back when in OS/390 R7 DFSMS 1.5 IBM changed the way HFS buffers were handled to default to half the storage on an LPAR. What a default! Combine increased use of HFS with LPARs with lots of storage (32GB or larger) and you get a really large working set for OMVS (6GB and growing when I reined it in). We should be converted to ZFS exclusively before this time next year but the HFS storage issue just showed up recently. We had put in R6 upgraded from R4 on this LPAR early this year and the mix of extended uptime, HFS using application growth and increased real storage sizes on a production LPAR really goosed the HFS appetite for buffers. The LPAR is a few weeks away from being IPLed and upgraded to R7. This is not new news but something to check that maybe didn't get done or left to default when OS/390 R7 was done. It is too old to get visibility in any current migration publications but might show up on your system as you keep adding storage for DB2 or other applications to exploit. http://www.ibm.com/support/techdocs/atsmastr.nsf/WebIndex/FLASH10021 Abstract: With OS/390 Release 7, the Hierarchical File System, (HFS), may use more buffers. IBM recommends you monitor the virtual storage usage and paging of your OS/390 system. If virtual storage usage is significantly higher after migration to OS/390 2.7, adjustments to the value on the VIRTUAL parameter may be required. VIRTUAL(max) is a parameter found on the BPXPRMxx FILESYSTYPE statement. It specifies the maximum amount of virtual storage (in megabytes) the HFS cache should use. The amount of storage needed depends on the workload and system configuration. If you do not specifically set a value for VIRTUAL(max), the system assigns to max a default value which is equal to half the amount of central storage available to the OS/390 image at HFS initialization. The minimum amount of buffers which can be defined is 32MB. The file system will only use the amount of storage it needs up to the limit set by VIRTUAL(max). Note: The sample BPXPRMxx parmlib member provided in SYS1.SAMPLIB takes the default. It is highly recommended installations review the potential for increased HFS buffers, and how the increased virtual storage usage may affect the current system. The maximum limit can be changed dynamically by invoking the confighfs shell command. Use of this command is described in OS/390 UNIX System Services Command Reference. The code for the confighfs command is contained in the /usr/lpp/dfsms/bin directory. Additional information is available on how to set and measure the HFS buffer definition in Hierarchial File System Usage Guide, SG24-5482-00. Also with closed APAR OW38302, additional information on the definition and use of the output of confighfs command can be found in DFSMS publication Using Data Sets, SC26-4922. RMF will also provide HFS usage information via the SMF 74, subtype 6 records. This data can be viewed by using the RMF postprocessor HFS Report. Installations may be especially susceptible to the default specification if they do their migration testing on a system image with less available central storage configured than the target production system. Production systems will generally have more central storage configured, and/or have higher contention for the central storage. If you find your system is using more buffers due to heavy I/O to the HFS, and processor storage contention exists, setting a lower value on the VIRTUAL parameter may relieve this situation. For example, S/390 laboratory testing showed decreasing VIRTUAL(max) to approximately 100MB still supported a very high throughput to the HFS cache. >From the WSC site - Techdocs - the Technical Sales Library http://www.ibm.com/support/techdocs/atsmastr.nsf/Web/Techdocs Best Regards, Sam Knutson, GEICO Performance and Availability Management mailto:[EMAIL PROTECTED] (office) 301.986.3574 "Think big, act bold, start simple, grow fast..." ==================== This email/fax message is for the sole use of the intended recipient(s) and may contain confidential and privileged information. Any unauthorized review, use, disclosure or distribution of this email/fax is prohibited. If you are not the intended recipient, please destroy all paper and electronic copies of the original message. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
