On 12/30/2010 04:20 AM, James wrote:
Can someone point me in the right direction? (a) what causes these errors precisely? (b) is the error benign? How can I determine if it is *likely* a hardware problem? (I imagine it's probably impossible to tell if it's HW until it's too late) (c) are these errors expected in a RAID array that is heavily used? (d) what kind of errors should I see regarding "read errors" that *would* indicate an imminent hardware failure?
(a) these errors usually come from defective disk sectors. raid recostructs the missing sector from parity from other disks in the array, then rewrites the sector on the defective disk; if the sector is rewritten without error (maybe the hd remaps the sector into its reserved area), then just the log messages is displayed.
(b) with raid-6 it's almost benign; to get troubles you should get a read error on same sector for >2 disks; or have 2 disks failed and out of the array and get a read error on one of the other disks while recostructing the array; or have 1 disk failed and get a read error on same sector on >1 disk while recostructing (with raid-5 it's almost dangerous instead, as you can have big troubles if a disk fails and you get a read error on another disk while recostructing; that happened to me!)
(c) no; it's also a good rule to perform a periodic scrub of the array (check of the array), to reveal and correct defective sectors
(d) check smart status of the disks, for "relocated sectors count"; also if md superblock is >= 1 there is a persistent count of corrected read errors for each device into /sys/block/mdXX/md/dev-XX/errors, when this counter reaches 256 the disk is marked failed; ihmo when a disk is giving even few corrected read errors in a short interval its better to replace it.
-- Yours faithfully. Giovanni Tessore -- 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
