Tino Schwarze wrote:
>
> My impression is that it scales so badly because there are a lot of
> seeks between pc backup directories and the pools. The MD5 hashing
> distributes files randomly over the pool, so you end up looking at
> another place on disk for each file which involves seeking.
>
> I've got a Dell machine here with PERC5/i (which is by no means fast)
> and I also have three WD RAID Edition 500 GB SATA drives. Somehow it
> doesn't fit very well. I'm seeing I/O starvation, throughput is at about
> 300-500 kB/s during backups and device utilisation is at 100% (measured
> with iostat).
Small writes on raid5 always have a performance hit.
> I've got a second RAID5 on the same controller, but with three 750 GB
> SATA drives (Hitachi HUA721075KLA330). This seems to perform better, but
> mainly takes large files, so the seeking is not a problem. I wish there
> was a "swap file systems" operation so I could test how BackupPC
> performs on the second RAID. Hm. Maybe I'll use a weekend to copy the
> raw xfs file system to another logical volume? But then there's still
> the file system tuning issue. Or I'm just suffering partition
> misalignment so FS accesses cross RAID stripes too much? So much
> questions, so little time... :-(
Big writes aren't quite so bad. But you would probably get much better
performance if you had 6 identical drives running in a striped/mirrored
configuration (at some cost in disk space).
> Or maybe I've just got too little memory? I see only 600MB of "cached"
> memory while the backup (our largest one: 2.9 million files, 120 GB)
> takes 640 MB plus 480 MB for each of the BackupPC_dump processes (using
> rsync). The machine has 2 GB.
If you aren't actively swapping, the ram is probably OK. Unless you
have slow network links you will probably want to only run 2 backups
concurrently.
--
Les Mikesell
[EMAIL PROTECTED]
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