[DRBD-user] suffering from iowait

Wolfram Schlich lists at wolfram.schlich.org
Fri Aug 15 00:04:47 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.


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

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)?

Wolfram Schlich <wschlich at gentoo.org>
Gentoo Linux * http://dev.gentoo.org/~wschlich/

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