>-----Original Message-----
>From: Les Mikesell [mailto:lesmikesell AT gmail DOT com]
>Sent: Tuesday, May 11, 2010 5:07 PM
>To: backuppc-users AT lists.sourceforge DOT net
>Subject: Re: [BackupPC-users] [Solved] Slow web-GUI access
>
>Read access is normally OK on a raid5. The issues are that with a small
>number of drives you essentially force all the heads to seek together to
>handle writing the parity and on partial block writes you have to read
>first, then rewrite to update the parity. So you slow down to the seek
>time of the slowest drive. If you noticed speed issues even when
>backups were not writing to the array you probably had some other
>problem. Did you check (cat /proc/mdstat) to make sure all the drives
>were working? Perhaps it was running degraded and your eventual failure
>was when a 2nd drive dropped out.
So was my understanding too; that raid5 read performance was ok.
What is a small number of drives? I have three identical 500GB Seagates of the
SATA2 variety, all bought new late last year, so I'm assuming fairly modern as
well.
My checks in /proc/mdstat showed nothing unusual. They've been working fine
all the time, all three of them; ie none is failed.
The backup of the linux machines here, is for the most part hundreds of
thousands of really small files, like in the 10-100kB-range. Could this be a
reason for slowness? I'm thinking that with so many small files, the write
portion of the backup can't really "take-off" as it would with a really big
files. Or maybe it doesn't really matter. This whole thing with what
filesystem to use etc depends a lot on what you're planning to backup. I have
most of everything, really small files all mixed up with really enormous ones.
--
/Sorin
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