Re: [BackupPC-users] Tuning for disk contention

On Fri, Sep 4, 2009 at 4:05 PM, Michael Stowe <mstowe AT chicago.us.mensa DOT org> wrote:

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.

I have to agree. you will need to just start at 1 and move up.

What filesystem are you using? some are faster than others. If you are using ext3 then I suggest you try XFS.

Also, do you know what IO scheduler you are using? This can determin how gracefull your system behaves during high IO loads and can help keep your system load in check.

How are your disks setup? Are you doing raid? if you are doing raid5 or raid6, especially in software, that is a major point of slowdown. raid5/6 does a checksum that hurts performance significantly. Your best bet is to do either a raid1 mirror, or a raid10. no checksum while keeping redundancy.

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