Ciro Iriarte wrote: > 2007/10/26, Greg Freemyer <[EMAIL PROTECTED]>: >> On 10/25/07, Ciro Iriarte <[EMAIL PROTECTED]> wrote: >>> Anybody has experience with linux Raid5 and power outages?, i >>> currently have two 250GB disks in a RAID1 array in my main >>> workstation. When there's any power outage the array is rebuilt but >>> given it's a mirror it's not a major issue. >>> >>> Now i would like to add 4 500GB disks in a secondary array with raid5 >>> but i'm afraid i would lose the array if there's any outage (have to >>> mention a UPS in my letter to Santa....) >>> >>> Anybody knows if the raid5 (md) would survive this scenario? >>> >> The raid should definately survive, but the portion you are writing at >> the time could easily be corrupt. > > I thought that that kind of corruption would trigger the array rebuild > or logical fail... > >> Raid5 typically has a 64k per disk data unit, but your issues are >> going to really be at the 4k page level I think. >> >> In particular, when you write/overwrite a page the kernel has to read >> the original page of data and the checksum page of data. Update both >> and write them both back out. There is really no way the OS can >> ensure that both writes actually make it to disk simultaneously. >> >> So if you have a power outage while writing to a raid5 the odds are >> high that one of the 2 updates failed to make it to disk. The good >> news, is the array itself should be fine. It just the single raid5 >> stripe that is corrupted. You likely won't find out about the problem >> until you lose a disk. But even then it will just be a few pages that >> are impacted. > > So?, i will just heal itself?, continue to work with some corrupted > files (corrupted stripe effect)?
Hi Ciro, Try to think of a RAID Array as a single partition. You put a filesystem "on top" of a partition or a RAID Array. If the power fails, the -partition- DOES "survive". The filesystem may have inconsistencies but it is probably recoverable. It is the same principle ( almost ) with a Soft-RAID array. If you have frequent power loss, IMHO, you should activate RAID write-intent bitmapping. The command is mdadm /dev/mdX -Gb internal If you are afraid about a RAID's inconsistency by issuing "echo check >> /sys/block/mdX/md/sync_action" and check for failures wiht "cat /sys/block/mdX/md/mismatch_cnt". If there are failures, correct it with "echo repair >> /sys/block/mdX/md/sync_action" You can also put it on a cron script... Hope it helps, Rui > >> Greg >> > > Regards, > Ciro -- Rui Santos http://www.ruisantos.com/ Veni, vidi, Linux! -- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
