[DRBD-user] Performance Issue - HP cciss

Ben Clewett ben at roadrunner.uk.com
Wed Jan 30 15:48:51 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.

Matteo Tescione wrote:

Hi Matteo,

Thanks for your advise, I'll give that a go.  Very glad to hear I am not 
the only person with these problems!

Changing RAID is not hard.  I have upgraded the firmware once, I'll try 
it again.  My system reports me on firmware 4.12.

I have also found this posting which shows my exact symptoms, might be a 
help to both of us:




>> Lars Ellenberg wrote:
>>> 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.
>> Oh well, back to the drawing board.
>> I think changing the read-ahead value might have caused the disk
>> controller to re-start, therefore unlocking what ever was stuck on the
>> card.  In which case I could just change this value from 'cron' every
>> hour and never see this problem again :)
>>>> Thanks again for your excellent analysis,
>>> we also do support and consulting, you know :)
>> It may come to that, and I am happy to contract you if need be.  However
>> I still have a few options, and I would like to fix it my self.  I have
>> to maintain these objects of delight, and this is a good way of learning
>> how they work, or not work :)
>> I'd like to ask the group if any owners of HP cciss disk controllers
>> have experienced similar locking, evident by 100% 'iowait' on both sides
>> of a DRBD connection.  If so, can they mail be the version they have and
>> how they fixed it please?
> I did. I runned in really deep troubles few months ago with a p400 array
> from dl320s servers. 100% util and very poor performance about 10-20 mb/s.
> I didn't find a true solution, but i discovered 2 workaround:
> 1. changed the raid level from 5/6 to 10 because of the slow latency disk
> operations. See the post "performance solved"
> 2 upgraded the p400 firmware twice. I had to download 2 cd's from hp with
> very important fixes in their controller, like introducing sata command
> queue and many others.
> Hope this helps,
> Regards,
> --
> #Matteo Tescione
> #RMnet srl

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