Does the tape subsystem have physical tape cartridges? If so, then tape mounts are probably a big part of the time involved. I can only speak to the IBM TS 7700 I last used before I semi-retired, which had high-capacity tape cartridges.
1. Scratch tapes are 'fast ready' (I think that's the term) - there's no mount time as long as your disk cache has space for virtual tapes. So writing a bunch of tapes incurs very little mount time. 2. When doing a restore, first you load the physical cartridges into the VTS before you ever start any jobs. 3. When you run the restore job, there's _nothing_ in the disk cache. 4. Therefore, every virtual tape mount is a cache miss and requires a recall. 5. Recall is a mount, fast forward to the virtual tape's position, reading the virtual volume from the tape and writing it to the disk cache, _before_ your virtual mount is satisfied. 6. If you run multiple restore jobs, and they refer to virtual tapes on the same physical cartridge, you will have contention for the physical tape (which you don't see in any monitor on zOS! )and one job's virtual mount will have to wait on the other one's. As you can see there are quite a few delay points in a restore. I created a SHARE enhancement request (in the Storage project) that I hope IBM will implement, which would help with some of these delays. Basically, it would be an HMC enhancement on the VTS so that you could indicate that you are loading tapes for DR, and when that indicator was set, each tape loaded would immediately be mounted, and have its virtual tapes written to the disk cache, up to some threshold of the cache. Doing so would help alleviate the problems in 3, 4, 5, and 6. I don't know of good ways to pre-mount the tapes and therefore pre-load the cache from zOS but it might be possible. It's also possible, if you use BVIR to retrieve data telling you which virtual tape is on which physical cartridge, to try to split your restores by physical cartridge to try to eliminate some of the physical mount contention. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
