Someone once observed that 'rarely used' is not the same the thing as 'lightly used'. Whenever a file is accessed for read or write, IOS goes after it with a heavy boot. Then there's the problem of backups: if a file is worth keeping around, you probably want to back it up periodically, maybe even frequently. Files like JES checkpoint and couple data sets do not appreciate being made to stand in line even for seconds.
The biggest advantage of large volumes is reduction in UCB count. One disadvantage is that larger volumes take longer to back up and to restore. We have some astonishingly large 'volumes' in the open systems world that are supported by only modestly fast backup/restore processes. Keeping an important application down for a lengthy restore is a hard bullet to bite. . . JO.Skip Robinson Southern California Edison Company Electric Dragon Team Paddler SHARE MVS Program Co-Manager 626-302-7535 Office 323-715-0595 Mobile [email protected] From: "Lester, Bob" <[email protected]> To: [email protected], Date: 02/22/2013 12:54 PM Subject: Re: Mod-9 vs. Mod-27 vs. mixed Sent by: IBM Mainframe Discussion List <[email protected]> Hi, In our environment, we have a mix of emulated 3390-9 and 3390-54. When we have a need for small volumes (page, etc), we use 3390-9s and backfill them with rarely referenced files - documentation, etc. I tend to keep the system on 3390-9s (except SMPPTS!), as there was (once) a bit of a performance hit on the emulated 3390-54s. Not sure if that's still true. The physical drives are 650GB, and with the cache in front of them, I'm not sure it matters anymore. I'd be interested to hear opinions on this. Thanks! BobL -----Original Message----- From: IBM Mainframe Discussion List [mailto:[email protected]] On Behalf Of Skip Robinson Sent: Friday, February 22, 2013 1:40 PM To: [email protected] Subject: Re: Mod-9 vs. Mod-27 vs. mixed [ External ] In the interest of frugality, I asked my storage guys some time ago to allocate some tiny volumes for JES checkpoint and couple data sets. After a while, they complained that it was more trouble than it was worth because we mirror most volumes to the DR site. For every tiny source volume, they needed a corresponding tiny mirror volume. Periodic DASD refresh (aka upgrade) projects only added to the complexity. Pennies vs. pounds. . . JO.Skip Robinson Southern California Edison Company Electric Dragon Team Paddler SHARE MVS Program Co-Manager 626-302-7535 Office 323-715-0595 Mobile [email protected] From: "Staller, Allan" <[email protected]> To: [email protected], Date: 02/22/2013 10:04 AM Subject: Re: Mod-9 vs. Mod-27 vs. mixed Sent by: IBM Mainframe Discussion List <[email protected]> Space wasted for "small volumes" e.g. XCF couple datasets. Just a talking point. With Hyper-PAV, etc. most of the other points are just "hot air". The convenience of not having to support multiple "geometries". <snip> A client with DS8000 DASD configured as a mix of 3390 Mod9 and Mod27s is considering a project to convert everything to Mod-27. Does anyone out there have some thoughts on the advantages or disadvantages of this? I'm not looking to start a religious discussion or other "dinotribe," so feel free to respond to me privately. I'm just interested in perspective and talking points, either way. </snip> ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
