[CentOS] High load averages with latest kernel and USB drives?

Amos Shapira amos.shapira at gmail.com
Thu Nov 19 07:20:00 UTC 2009


Sorry can't suggest much about the usb issue but for such frequent
backups, as well as to enable poin-in-time-recovery (PITR) you should
consider log archiving. It should also save you heaps of load on cpu,
disk, network and postgresql server.

-Amos

On 11/17/09, Benjamin Smith <lists at benjamindsmith.com> wrote:
> I'm having a server report a high load average when backing up Postgres
> database files to an external USB drive. This is driving my loadbalancers
> all
> out of kilter and causing a large volume of network monitor alerts.
>
> I have a 1TB USB drive plugged into a USB2 port that I use to back up the
> production drives (which are SCSI). It's working fine, but while doing
> backups
> (hourly) the load average on the server shoots up from the normal 0.5 - 1.5
> or
> so up to a high between 10 and 30. Strangely, even though the "load is high"
> the server is completely responsive, even the USB drives being accessed are!
>
> Backup script is really simple, run via cron, pretty much just:
>
> #! /bin/sh
> hour=`date +%k`;
> pg_dump <options> mydatabase > /media/backups/mydatabase.$hour.pgsql;
>
> where /media/backups is the mount point for the USB drive.
>
> Using top to diagnose, nothing seems to be particularly high! IoWait seems
> reasonable (10-30%) and CPUs are 0.5%, Idle is 70-90%. Even accessing the
> USB
> partition while the load is "high" is responsive!
>
> I'm guessing that something changed in how load average is counted?
>
> Server Stats:
> 	Late model 8-way Xeon, SuperMicro brand.
> 	CentOS 4.x  / 64 (all updates applied, booted after last kernel update)
> 	Kernel 2.6.9-89.0.16.ELsmp
> 	4 GB ECC RAM
> 	300 GB SCSI HDD.
> 	Standard Apache/PHP, Postgres 8.4.
>
> Any idea how to revert to the old load average tracking behavior short of
> using a stale and potentially insecure kernel?
>
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