>-----Original Message----- >From: Les Mikesell [mailto:[email protected]] >Sent: Tuesday, May 11, 2010 5:07 PM >To: [email protected] >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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