Vincent Fox wrote: >David Lang wrote: > > >>raid 6 allows you to loose any two disks and keep going. >> >> >> >> > >This is turning into a RAID discussion. > >The orginal poster was doing a RAID-5 across 3 disks, and has stopped >commenting but it's probably because that's all the hardware he could >scrounge. > > > > > The "original poster" (me) has not commented further on the RAID discussion that has evolved from my initial questions because we are in fact limited in what we can afford. The points on the relative crappiness of RAID5 have been very illuminating and useful, however. Yesterday, we moved the cyrus metadata off the md->drbd->lvm->ext3 partition onto a vanilla ext3 one (in fact, on the system PATA disk) and have seen modest improvement as measured by average system load and user contentment. Our intent is next to junk the RAID5 and go with a simple mirrored pair of 500Gb SATA disks for the mailspool and a second mirrored pair for the metadata. We had wanted the potential for automatic fallover with drbd but will scrap that for now. We are planning to run the mirrors off a 4-port 3ware RAID card even though we're not overly fond of 3ware (we have a fair amount of experience with RAID5 arrays on 3ware cards on our research machines where they perform adequately but not more). We are hoping the 3ware RAID1 will be a bit better than software RAID1. I would also like to comment at this point that the lvm2 layer in our original design was so that we could use snapshots to insure a static filesystem for backups. So a secondary question concerns how much potential troubles we might have just backing up (with rsync) the active system? Thanks again for everyone's insight and suggestions. Once the production system is working better and users have been pacified, we'll continue to tinker with the lvm and drbd layers on a pair of test machines, but without RAID5. I don't really think those other layers are the show-stoppers, although it is certainly true that the combined effects of the incremental inefficiencies of each layer might have had cumulative impact. I note in passing that we had tested the original design by pounding the pair of machines with incoming mail and that did not reveal the gross difficiencies that we saw when we started accepting user imap connections as well. Can someone in fact suggest a good battery of testing software so that we don't prematurely certify that a new system is ready for production use (or a useful statistic to monitor)? Jeff Fookson -- Jeffrey E. Fookson, PhD Phone: (520) 621 3091 Support Systems Analyst, Principal jfookson@xxxxxxxxxxxxxx Steward Observatory University of Arizona ---- Cyrus Home Page: http://cyrusimap.web.cmu.edu/ Cyrus Wiki/FAQ: http://cyrusimap.web.cmu.edu/twiki List Archives/Info: http://asg.web.cmu.edu/cyrus/mailing-list.html
