(My origional post was rejected . . . I'm resending it)
I've been playing around with the same thing although in a completely different context. Although a better person should answer this, I believe the occ is what the TSM server sees - the byte stream into and out of the TSM server. If running client compression, then the server only sees the compressed data stream coming in. If compression at the tape drive, then tsm only see the data stream it sends to the drive, not what the drive does. But . . . this gets more complicated. Remember that the CDL emulates tapes - in all their details. This includes the need for expiration and reclamation. In other words, how full are your tapes? If you are running reclamation at, say, 60%, then you have up to 40% of many tapes unusable until reclamation is run. The CDL will work exactly the same way on it's virtual tape volumes. My understanding is that when a new virtual tape is created It grows the disk space allocated in chuncks (I thought I heard 5gb as a number once), so new tapes only use used space. But full tapes with expired data still use the full tape. So, your calculation might have to be something like . . . . .(thinking out loud . . . high possibility of error) . . . ( total-occupancy + total-expired-but-not-reclaimed-space ) / virtual-tape-drive-compression-ratio + some huge fudge factor. It is very possible with the CDL with growing new tapes by chunks to overcommit the CDL. You could end up with a situation with many TSM tapes that are FILLING, but have the CDL out of disk space. It does have the option to fully allocate the disk space for a virtual tape when the tape is created. Another thing to think about . . . . co-location. I've been thinking about this a lot. If we used s CDL, would I still want to co-locate our primary tape pools? Virtual tapes should mount very quickly. Seeking to the data on a virtual tape should be fast, although I haven't heard how the CDL implements seeks. So, can I do without co-location on the primary tape pool? I don't know . . .needs more thinking and probably testing (if we ever do this). Another thing to think about . . . . which library to emulate and how many. The list of libraries you can pick from to emulate is small. Since a storage pool has to live within one library, the number of virtual tapes in the library has to have the capacity for the storage pool (again, don't forget expired data). The CDL has a limit on the number of virtual volumes, libraries and drives. According to the data sheet from EMC's web site, the CDL supports "Configures up to 32 tape libraries, 256 tape drives, and 2048 cartridges with a single disk library system . . ". You are going to have to juggle your pool sizes, the library size and the number of virtual tapes. Much to think about. . . . . . . Rick ----------------------------------------- The information contained in this message is intended only for the personal and confidential use of the recipient(s) named above. If the reader of this message is not the intended recipient or an agent responsible for delivering it to the intended recipient, you are hereby notified that you have received this document in error and that any review, dissemination, distribution, or copying of this message is strictly prohibited. If you have received this communication in error, please notify us immediately, and delete the original message.
