[DRBD-user] Performance Issue - HP cciss

Lars Ellenberg lars.ellenberg at linbit.com
Wed Jan 30 13:17:03 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.

On Wed, Jan 30, 2008 at 11:12:54AM +0000, Ben Clewett wrote:
> 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?

since DRBD meta-data access most of the time is sinlge sector
synchronous IO, read-ahead is completely irrelevant here.

> Thanks again for your excellent analysis,

we also do support and consulting, you know :)

: Lars Ellenberg                           http://www.linbit.com :
: DRBD/HA support and consulting             sales at linbit.com :
: LINBIT Information Technologies GmbH      Tel +43-1-8178292-0  :
: Vivenotgasse 48, A-1120 Vienna/Europe     Fax +43-1-8178292-82 :
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