Workable copy pools is *possible*, provided all primary storage pool is on disk; that is, all backups go to disk pool, which is sufficiently large to hold all the versions for retention... and never does migration!
I've had to do this (and more) for a capital equipment-constrained customer; 12 locations around the world, getting the "same" equipment (from Dell) for service replacement purposes. Most sites had two drives (one in each 120T), one site had two drives in a single library (130T), but TWO SITES WITH SINGLE DRIVE LIBRARY needing onsite backups got 105 GB disk pool (sufficient to provide 14-day point-in-time restore for approx. 55-65 GB, depends on daily turnover)... so, with six usable slots, we configured 2-slots for onsite copypool, 2-slots for offsite copypool, 2 slots for db-backups. Reclamation was done as if both copy pools were offsite, so fresh tapes would be cut from the primary disk pool -- so, single drive reclamation was not required. For the 1-drive, 2-library sites, single drive reclamation was done AND it worked just fine (using 100 GB disk pool, scheduled for weekends after disk migration)... all these sites ran fine for over two years, the only true "glitches" were due to onsite tape management needing occasional assistance with their DRM actions. Also, turns out, we rarely had tape drive failure after the initial install/burn-in period -- even then, we had less than 5 drives fail across all 12 sites. NOT the *best* answers, but these configurations did allow us a lights-out environment --- biggest caveat is when (not if) the drive goes down, no backups to tape (slightly mitigated by using LAN to store db-backups off to another server). Yes, running with less than 3 drives is a challenge, but a lights-out setup *can* be done with only 1 drive PLUS a large disk pool for the primary storage pool! (My motto, had to be: "If you bring money, we can solve"!!!) Don France Technical Architect -- Tivoli Certified Consultant Tivoli Storage Manager, WinNT/2K, AIX/Unix, OS/390 San Jose, Ca (408) 257-3037 mailto:[EMAIL PROTECTED] Professional Association of Contract Employees (P.A.C.E. -- www.pacepros.com) -----Original Message----- From: ADSM: Dist Stor Manager [mailto:[EMAIL PROTECTED]]On Behalf Of Zlatko Krastev Sent: Saturday, August 17, 2002 8:09 AM To: [EMAIL PROTECTED] Subject: Re: 2 drives are required for LTO? Mark, I fully agree with your opinion. TSM *can* work with single drive but it would be ugly. Same waste of resources as assignment to 5k project a project manager with 300k salary (and you can always send 1 kg parcel with a truck). I said it is possible but will never say I recommend it. Zlatko Krastev IT Consultant Please respond to "ADSM: Dist Stor Manager" <[EMAIL PROTECTED]> Sent by: "ADSM: Dist Stor Manager" <[EMAIL PROTECTED]> To: [EMAIL PROTECTED] cc: Subject: Re: 2 drives are required for LTO? From: ADSM: Dist Stor Manager [mailto:[EMAIL PROTECTED]]On Behalf Of Zlatko Krastev > The requirement for 2 drives is not mandatory, it ought to be just a > suggestion. LTO can be used as a standalone drive, TSM can use single > drive or small autoloader with single drive. So it is NOT required but > recommended. Yes, technically a single drive is sufficient to do backups. But then I could use a pair of nail scissors to mow my lawn... > - single drive reclamation - define reclamation storage pool of type FILE. > On reclamation remaining data is moved to files and later written to new > tape volume. Drawback: data is not read when written (sequential > read+write vs. parallel) thus takes more time. Calculate time budget > around the clock. FILE storage pool-based reclamation is dog slow, and expensive of disk space, particularly if you are backing up database-type data of any size. I've got a customer trying to do this very thing, and reclamation is extremely slow. > - single drive copypools - define following hierarchy DISK -> FILE -> LTO > (file pool would be also lto reclamation pool). Prevent file->lto > migration during backups (highmig=100). Perform backups to copypool after > node backups finish. Allow migration after backup to copypool finishes. > Drawbacks: filepool must be large enough to hold all backups data. Backups > should not happen during migration because some object(s) may migrate > without being copied to the copypool. Again time - data have to be written > twice through the one-and-only drive. And on the end with one drive there > is no way to perform copypool reclamation. Bingo. A single tape drive, because of the lack of reclamation, means no usable copy pool, no way to use move data to consolidate primary tape volumes, and no way to use a restore volume command to rebuild bad primary pool media from copy pool media--in short, a badly crippled TSM backup system. > Conclusion: for a small installation data might be not too much, time > might be enough for all activities (node backups, copypool backup, primary > pool raclamation, migration, DB backup). Thus neither LTO technology nor > TSM dictate number of drives to be used but only the business requirements > you have. Don't let anyone tell you that a single tape drive is adequate for anything resembling a real backup system. If you can't afford a real library, you can't afford a real backup system. My experience with multiple environments calls for a minimum of three drives--two drives for multitape operations, and a spare in case one drive breaks down. -- Mark Stapleton ([EMAIL PROTECTED]) Certified TSM consultant Certified AIX system engineer MCSE
