[DRBD-user] Identifying High iowait on DRBD Computers

Robinson, Eric eric.robinson at psmnv.com
Thu Feb 17 16:43:00 CET 2011

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

This iowait thing is driving me batty. The system was running fine for a
long time at about 1-7% iowait except during backups. During backups
iowait is usually pegged at 25%. But recently, the system has started
running at 25% iowait all the time, with periods of 50% iowait and peaks
of 70-90%. This is a relatively sudden development.
The server is 4-core PowerEdge 2950 with 8GB of RAM and 6x300GB 7.5K SAS
drives in a RAID 5 array. All it does is FTP. It peaks at about 250
concurrent FTP users. Average file size is about 80K. The backing device
for drbd0 is a 2TB LVM partition. The filesystem is ext3. Since
kjournald is the biggest consumer of disk iops, I will soon change the
filesystem to mount with 'noatime'. 
Any ideas? Is there something about using LVM+drbd+ext3 with a 2TB
partition (1.3TB used) that causes a sudden jump in disk wait? 

Eric Robinson















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