Furthermore, drives (including those with SMART support) only reallocate bad blocks following write errors. A scrub/verify tool would be looking for read errors and would need to actively replace the unreadable block with rudundant data from a _different_ drive. Actually, I guess it would be kind of complicated. A scan for unreadable blocks would need to occur outside of the md layer (to prevent the errors from triggering a degraded state), yet the block replacement would need to occur through the md layer, since only md knows how to recreate the block from parity. It would probably be a easier for a RAID 1 array where the disks are symetric and you could guess the location of the redundant block on the second volume. You would probably need to use md on a RAID 5 array. -Kanoa On Sat, 7 Aug 2004, Salyzyn, Mark wrote: > Problem with running the relocation is that the RAID-5 will now be > corrupt. The RAID-5 algorithm needs to be in-touch with disk block > relocation so that it can correct the parity and the data. > > Sincerely -- Mark Salyzyn > > -----Original Message----- > From: dean gaudet [mailto:dean-list-linux-raid@xxxxxxxxxx] > Sent: Friday, August 06, 2004 5:59 PM > To: Kanoa Withington > Cc: Salyzyn, Mark; Derek Listmail Acct; linux-raid@xxxxxxxxxxxxxxx > Subject: RE: Scrub? > > On Fri, 6 Aug 2004, Kanoa Withington wrote: > > > On Fri, 6 Aug 2004, Salyzyn, Mark wrote: > > > Just reading the entire array should correct the bad blocks, so > reverse > > > the sense of the dd: > > > > > > dd if=/dev/md0 of=/dev/null bs=200b > > > > > > to find and replace the bad blocks (making the assumption that md > works > > > like the H/W RAID cards). > > > > In this case software RAID does not work like the H/W cards. Finding > > an unreadable block that way in a software array would cause it to go > > into a degraded state. > > if the disks support SMART (i.e. they're less than a few years old) then > try running the smart long selftest... it can be done online and on many > disks it will force sector reallocation (and produce a SMART log event > so > you know it happenned). > > get smartmontools and run "smartctl -a" to see info on your drive, and > "smartctl -t long" to launch the long test. man page has more examples. > > i run smart long tests on each my disks once a week (staggerred over > many > nights)... see /etc/smartd.conf. > > -dean > - > To unsubscribe from this list: send the line "unsubscribe linux-raid" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
