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