Why does it check the parity and not just write the correct parity? Does it log the count that were wrong, or anything? And does your new --update=resync option do the same thing? Thanks, Guy -----Original Message----- From: linux-raid-owner@xxxxxxxxxxxxxxx [mailto:linux-raid-owner@xxxxxxxxxxxxxxx] On Behalf Of Neil Brown Sent: Thursday, August 19, 2004 9:21 PM To: PAulN Cc: Guy; linux-raid@xxxxxxxxxxxxxxx Subject: Re: Raid5 Construction Question On Thursday August 19, pauln@xxxxxxx wrote: > > md0 : active raid5 sdh1[7] sdf1[6] sdg1[5] sde1[4] sdd1[3] sdc1[2] > sdb1[1] sda1[0] > 481949184 blocks level 5, 64k chunk, algorithm 2 [7/7] [UUUUUUU] > [>....................] resync = 2.4% (1936280/80324864) > finish=4261.4min speed=305K/sec > > In the docs I saw that "reconstruction" is possible with raidhotadd but > I didn't > see anything about initialization. So am I "screwed" until the resync > is fixed? I was depeding > on the disks to do some filesystem testing but maybe I'll have to wait a > few days.. When resyncing an array, raid5 will read all the blocks in each stripe, check the parity, and if it is wrong, write out the new parity. For a mostly-correct array this just involves lots of sequential reads. For a mostly incorrect array, this involves lots of read-seek-writes which is substantially slower. When reconstructing onto a spare, raid5 will read all the good drives and write to the spare. This all IO is sequential, there are no seeks, and it is nice and fast. It is for this reason that 'mdadm' will normally create a raid5 array with one missing drive and one spare, which is then immediately reconstructed. mkraid, on the other hand, doesn't know about this, and just creates the array and the sync happens which, as you note, can be quite slow. So, you can either re-make the array with mdadm or, you can fail one drive, remove it and re-add it. raidsetfaulty /dev/md0 /dev/sdh1 raidhotremove /dev/md0 /dev/sdh1 raidhotadd /dev/md0 /dev/sdh1 In either case it should stop the resync and start reconstruction which will be much faster. NeilBrown - 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
