[DRBD-user] suffering from iowait

Mark Watts m.watts at eris.qinetiq.com
Fri Aug 15 09:51:30 CEST 2008

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.

On Thursday 14 August 2008 23:04:47 Wolfram Schlich wrote:
> Hi,
> imagine the following setup:
> - 2 node cluster
> - 2x Dell PowerEdge 860, Dual Core Xeon 2.13GHz,
>   4GB RAM, SATA HW RAID1 (write cache enabled,
>   NCQ enabled), 1GE link for internal cluster
>   communication (DRBD, Heartbeat etc.), Heartbeat
>   fencing using IPMI-over-LAN
> - Linux 2.6.25 x86_64 with deadline or CFQ scheduler
>   (tried both)
> - DRBD 8.2.6
> - Heartbeat 2.1.3 with dopd enabled
> - drbd.conf: see http://paste.frubar.net/8786
> - MySQL-5.0.60 with sync-binlog=1 and
>   innodb_flush_log_at_trx_commit=1
> With the DRBD instances connected, the system
> spends >30% on iowait and is >30% idle
> during a load test.
> With the secondary instance disconnected, the system
> does (almost) not spend any time on iowait, CPU
> usage is at around 80% user and 20% system, but
> the load goes slowly up to more than 20 after a
> minute or so...
> What could be the reason for both issues (iowait
> vs. load skyrocketing)?
> Thanks!

If its like other Dell's, you should start by disabling the TCP Offload (TOE) 
by removing the hardware key on the motherboard.


Mark Watts BSc RHCE MBCS
Senior Systems Engineer
QinetiQ Applied Technologies
GPG Key: http://www.linux-corner.info/mwatts.gpg
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