True. ... I use the reuse delay on my copypool tapes (same number of days that I keep db backups). But on my onsite tapepool, I use a reuse delay of zero, making them immediately available. It may not be advisable, but with a small library, sometimes you do things that way :(
-----Original Message----- From: Johnson, Milton [mailto:[EMAIL PROTECTED] Sent: Wednesday, September 01, 2004 1:30 PM To: [EMAIL PROTECTED] Subject: Re: Sizing for a virtual tape library Just to add another fly in the ointment, if you have an aggressive reclamation threshold, say 25%, and a reuse delay of say 5 days, you may end up with a lot more tapes in a pending state then you anticipated. A pending tape is not a scratch tape. H. Milton Johnson -----Original Message----- From: ADSM: Dist Stor Manager [mailto:[EMAIL PROTECTED] On Behalf Of Coats, Jack Sent: Wednesday, September 01, 2004 12:42 PM To: [EMAIL PROTECTED] Subject: Re: Sizing for a virtual tape library I agree, think of it as so many tapes. Since they are 'really fast tapes', being on disk, you might consider doing reclaimation at some unusually low number to get expired data out of the way ASAP. If you don't need the space that badly, relax the reclaimation percentage a bit. Instead of starting withe 80 or 60 percent like you would on tapes, you might start with 40 percent and go to 20 percent if you need the space. This still leaves you with about 20% of the library with 'old data', plus your need for at least one or two 'scratch tapes' in the library at a minimum! If emulating LTO1 drives, at 100G each, 62T gives you about 600 (being conservative) volumes. Take away even 2 scratch volumes as a minimum for scratch tapes and subtract 20% of the rest as 'expired data' you still get (598 - 120) 478 volumes at 100G each of real data, or 47.8T on your 62T library. If you know your data, and know you get a real world 30% compression, then it should find close to your 62T of data ( 47.8*1.3=62.14T but that is close with this level of engineering estimate). If you get better compression you really win. Depending on your needs, you could use client compression, or tape drive compression. There are religous camps on both sides, but I suggest you give it a try both ways to see what you really get. ... green with envy ... JC
