[DRBD-user] Performance Issue - HP cciss

Ben Clewett ben at roadrunner.uk.com
Wed Jan 30 12:12:54 CET 2008

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

Hi Lars,

I am still having performance issues, ref DRBD locking.  You were kind 
enough to spend some time to worked out it was probably my underlying 
storage at fault.

I am using HP cciss P400 hardware RAID controllers.  I have these in 12 
HP Proliant DL G5 servers, only four of these are on DRBD.  These four 
are the ones which suffer the problem.

I have recently changed the read-ahead-buffer from the default 4 MB to 
512 KB.  Therefore when the disk reads 1 or more bytes, it used to read 
another 4 MB into cache, and now reads 512 KB.  I can't take these 
servers off line to rigorously test, but anecdotally this seems to have 
made a difference for the better.

I note my meta-disks are covered by this read-ahead-buffer.

Do you think this might effect DRBD in some scenario?

If you had to suggest a read-ahead-buffer size for the meta-disk, can 
you suggest what might be optimum?

Thanks again for your excellent analysis,


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