Hi,
Thanks a lot for your answers.
I will work in considering your answers. It's very interresting.
Thanks.
Romain
Tino Schwarze
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Re: [BackupPC-users] Using a NAS
01/04/2008 10:35 Server to backups
On Tue, Apr 01, 2008 at 09:56:27AM +0200, Ronny Aasen wrote:
> > So, it works with NFS ?
>
> Yes it works with NFS. But it scales poorly
>
> I am running a small installation. only 23 hosts. on a 6TB nfs nas,
> using mostly gigabit ethernet.
> 5.9T 3.4T 2.6T 57% /var/lib/backuppc
>
> speed varies between 1 MB/sec and 8MB/sec with the average laying about
> 3MB/sec for a full backup. and 0.5MB/sec for incremental
>
> cpu is often in iowait during backups.
>
> mark: this is all server hardware intel server gigabit network cards.
> and lsi sas raid controller with sata 500GB raid edition harddrives
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).
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... :-(
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.
Bye,
Tino.
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