It's an awfully good question, but there probably isn't a single right
answer. My server is a quad-cpu beast on a gigabit network, but I settled
on two backups at a time after measuring degradation (first back up one at
a time, then two, then three...) Then again, neither my file system nor
server is dedicated, and for me, that means that other I/O bound processes
don't have trouble running.
Naturally, your I/O wait will be higher if your CPU's are faster, and load
average can be nonsensical if you're significantly I/O bound -- so I'd
recommend doing something similar to what I did -- namely, try one backup
at a time, then ratchet up the number until they slow down too much.
Filesystem type and physical storage structure are significant in how much
I/O overhead you've got.
> The discussion over the various BackupPC scenarios got me to
> thinking. My server IS disk bound. All the servers it backs up on on
> at least a 100M network link in the same room and some on 1G. With
> the default settings (4 simultaneous backups), the system is sitting
> right now at load average 9.25 and IO/wait from 33-99%. How does one
> best determine the fastest way to configure for the given scenario.
> Based on one respondent's comments, it makes me think I might be
> better off having only 1 backup running at a time?
>
> What's a good IO/WAIT average to shoot for? Load average? Other
> things I might not be thinking of?
>
> Thanks in advance,
>
> James
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