ADSM-L

Re: D2D vs. tape backups with TSM?

2004-07-22 12:05:22
Subject: Re: D2D vs. tape backups with TSM?
From: asr AT UFL DOT EDU
To: ADSM-L AT VM.MARIST DOT EDU
Date: Thu, 22 Jul 2004 12:05:07 -0400
==> In article <Pine.LNX.4.60.0407211614300.12323 AT zeus.itg.uiuc DOT edu>, 
Alexander Lazarevich <alazarev AT ITG.UIUC DOT EDU> writes:


> Does any TSM'er use disk based backup?

We've considered it, and are experimenting.  Here's what to keep you eyes out
for:


- Sustained outgoing bandwidth
- Sustained outgoing bandwidth in multiple streams
- Sustained outgoing bandwidth when other stuff is writing


So far, my observation is that, if I can just line the tapes up correctly,
restoring filesystems from tape is as fast or faster than disk.  This
distinction gets thrown into -sharp- relief if you have to do more than one
restore at a time.  If you've got (say) 85MB/s bandwidth out of your disk
plant that may seem nice, but if aggregate bandwidth for three restores is
still only 85, that might quickly become a problem.

Even more importantly, if you're restoring and someone backs something up, in
some architectures this totally blows out your cache, and you get big
bandwidth hits.

Not to sound too mantra-like, consider the restore case first: that's when
you're really going to care about it.  Assemble your 85% confidence-interval
worst case restore scenario, and subject your loaner infrastructure to it.


- Allen S. Rout

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