[CentOS] Re: DRBD NFS load issues

[Ugo Bellavance]

Jed Reynolds wrote:
> My NFS setup is a heartbeat setup on two servers running Active/Passive
> DRBD. The NFS servers themselves are 1x 2 core Opterons with 8G ram and
> 5TB space with 16 drives and a 3ware controller. They're connected to a
> HP procurve switch with bonded ethernet. The sync-rates between the two
> DRBD nodes seem to safely reach 200Mbps or better. The processors on the
> active NFS servers run with a load of 0.2, so it seems mighty healthy.
> Until I do a serious backup.
> 
> I have a few load balanced web nodes and two database nodes as NFS
> clients. When I start backing up my database to a mounted NFS partition,
> a plain rsync drives the NFS box through the roof and forces a failover.
> I can do my backup using --bwlimit=1500, but then I'm not anywhere close
> to a fast  backup, just 1.5MBps. My backups are probably 40G. (The
> database has fast disks and between database copies I see run at up to
> 60MBps - close to 500Mbps). I obviously do not have a networking issue.
> 
> The processor loads up like this:
> bwlimit   1500   load    2.3
> bwlimit   2500   load   3.5
> bwlimit   4500   load   5.5+
> 
> The DRBD secondary seems to run at about 1/2 the load of the primary.
> 
> What I'm wondering is--why is this thing *so* load sensitive? Is it
> DRBD? Is it NFS? I'm guessing that since I only have two cores in the
> NFS boxes that a prolonged transfer makes NFS dominates 1 core and DRBD
> dominate the next, and so I'm saturating my processor.

Is your CPU usage 100% all the time?


Can you send us the output of vmstat -n 5 5
when you're doing a backup?

Regards,

Ugo