Collocation has nothing to do with it. It's the nature of TSM and the VTS that causes 'problems.' TSM likes to use all the space on a tape. TSM keeps writing to a tape until it hits end-of-volume (EOV), then asks for another tape with space on it or a scratch tape.
In a VTS, when you ask for a virtual volume to be mounted, if the data does not already reside in the VTS cache/disk, then ALL the data on the volume is recalled from the 'real' 3590 tape into the cache. If there's not room, then the VTS will remove existing data from the cache based on a LRU algorithm. If that data hasn't been copied to the 'real' 3590 volumes,that has to happen first. So, no instead of mounting a tape and positioning to the end of the data, you have to read the data from tape into the disk cache BEFORE you can do anything with it. So,as the amount of data on the volume grows, the amount of time it takes to perform the tape mount increases. Now when you append data to the virtual volume, the VTS now has to stage this data back out to the 3590 tapes...all of it. Not just the 'new' data you appended. So now you're writing back out up to a full 3490 amount of data to tape. Where the original data existed on tape is now unusable space. Just like in TSM where expired data on tapes becomes unusable and you need to reclaim. This happens in the VTS, too. You have regularly scheduled reclamation tasks, plus thresholds. So, the more you append data to existing volumes the more frequent you would need to run the reclamation. Just more overhead in the VTS. Plus by having to recall the virtual volume into cache before you can append to it, or even read from it may cause other data withing the VTS to be removed from cache. This could cause longer mount times for other applications/jobs streams. You would want to have a larger amount of disk cache within the VTS for a system used for TSM. TSM reclamation would drive this system crazy, too. Without collocation, think of how many input tape mounts it takes to reclaim your offsite storage pool(s). Each one of those 'mounts' would cause the VTS to read the data back into cache before it could be read by TSM. Plus the VTS doesn't know that there is only maybe 10% usable data on that virtual volume. As far as he's concerned, it's a full tape. Maybe for a small TSM system you could use a VTS, but TSM is not the right application for a VTS. IMHO that is. Bill -----Original Message----- From: ADSM: Dist Stor Manager [mailto:[EMAIL PROTECTED]]On Behalf Of David Browne Sent: Monday, April 29, 2002 12:35 PM To: [EMAIL PROTECTED] Subject: Re: AW: Device_Mountlimit_VTS So, if you turn collocation off will TSM perform better with the VTS? Will this be a big performance hit on the client restores? Schaub Joachim Paul ABX-PROD-ZH To: [EMAIL PROTECTED] <joachim.schaub@ cc: ABRAXAS.CH> Subject: AW: Device_Mountlimit_VTS Sent by: "ADSM: Dist Stor Manager" <[EMAIL PROTECTED] T.EDU> 04/29/02 09:59 AM Please respond to "ADSM: Dist Stor Manager" Thank you Bill we now about the constallation tsm-vts and are on the right evaluation path now (nativ 3590 drives for tsm?) with kind regards Joachim -----Urspr|ngliche Nachricht----- Von: Bill Boyer [mailto:[EMAIL PROTECTED]] Gesendet: Montag, 29. April 2002 15:52 An: [EMAIL PROTECTED] Betreff: Re: Device_Mountlimit_VTS I've seen TSM use more than the MOUNTLIMIT when high priority tasks need to be performed. But I question you're use of a VTS for TSM? There was just a long discussion on this a couple weeks back. Applications that use the entire media (DISP=MOD) like TSM and DFSMShsm are not really good candidates for a VTS. Check out the archives to review the thread. (http://www.adsm.org) When TSM wants to add on to an existing storage pool volume, the existing data must be transferred back into cache in the VTS before it can be appended. Then the 'new' volume has to be staged back to real 3590 tape. The original location on real 3590 is now unavailable and needs to be reclaimed. By doing this a lot, you are forcing the VTS to do a lot of reclamation tasks. Plus the mount wait time to stage the data is holding you up. Unles you write to a volume and mark it as read-only so TSM won't try to append to it again. Bill Boyer DSS, Inc. -----Original Message----- From: ADSM: Dist Stor Manager [mailto:[EMAIL PROTECTED]]On Behalf Of Schaub Joachim Paul ABX-PROD-ZH Sent: Monday, April 29, 2002 4:06 AM To: [EMAIL PROTECTED] Subject: Device_Mountlimit_VTS Dear *SM Gurus Our VTS has 64 logical drives, the mountlimit in this deviceclass is set to 38 in the TSM Server. Last Week i saw in the Mainvew Monitor an usage off 50 logical drives by TSM ! Is it possible to user more mountpoints, as they are defined by teh mountlimit? Env: TSM Server 4.2.1.9 OS/390 Thanks in advance Joachim ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Joachim Paul Schaub Abraxas Informatik AG Beckenhofstrasse 23 CH-8090 Z|rich Schweiz / Switzerland Telefon: +41 (01) 259 34 41 Telefax: +41 (01) 259 42 82 E-Mail: mailto:[EMAIL PROTECTED] Internet: http://www.abraxas.ch ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ =
