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? Thanks, Ben > ************************************************************************* This e-mail is confidential and may be legally privileged. It is intended solely for the use of the individual(s) to whom it is addressed. Any content in this message is not necessarily a view or statement from Road Tech Computer Systems Limited but is that of the individual sender. If you are not the intended recipient, be advised that you have received this e-mail in error and that any use, dissemination, forwarding, printing, or copying of this e-mail is strictly prohibited. We use reasonable endeavours to virus scan all e-mails leaving the company but no warranty is given that this e-mail and any attachments are virus free. You should undertake your own virus checking. The right to monitor e-mail communications through our networks is reserved by us Road Tech Computer Systems Ltd. Shenley Hall, Rectory Lane, Shenley, Radlett, Hertfordshire, WD7 9AN. - VAT Registration No GB 449 3582 17 Registered in England No: 02017435, Registered Address: Charter Court, Midland Road, Hemel Hempstead, Hertfordshire, HP2 5GE. *************************************************************************