Maarten said: "Normally, the minute a drive fails, it gets kicked and the spare would kick in and md syncs this spare. We now have a non-degraded array again." Guy says: But, you make it seem instantaneously! The array will be degraded until the re-sync is done. In my case, that takes about 60 minutes, so 1 extra minute is insignificant. Marrten said: "Yes, but this would be impossible to do, since md cannot anticipate _which_ disk you're going to fail before it happens. ;)" Guy says: But, I could tell md which disk I want to spare. After all, I know which disk I am going to fail. Maybe even an option to mark a disk as "to be failed", which would cause it to be spared before it goes off-line. Then md could fail the disk after it has been spared. Neil, add this to the wish list! :) EMC does this on their big iron. If the system determines a disk is having too many issues (bad blocks or whatever), the system predicts a failure, the system copies the disk to a spare. That way a second failure during the re-sync would not be fatal. And a direct disk to disk copy is much faster (or easier) than a re-build from parity. This is how it was explained to me about 5 years ago. No idea if it was marketing lies or truth. But I liked the fact that my data stayed redundant while the spare was being re-built. This would not work if a drive failed, only if a drive failure was predicted. Another cool feature... the disk array then makes a support call. The disk is replaced quickly, normally before any redundancy was lost. Guy -----Original Message----- From: linux-raid-owner@xxxxxxxxxxxxxxx [mailto:linux-raid-owner@xxxxxxxxxxxxxxx] On Behalf Of maarten Sent: Saturday, January 08, 2005 2:25 PM To: linux-raid@xxxxxxxxxxxxxxx Subject: Re: Spares and partitioning huge disks On Saturday 08 January 2005 19:55, you wrote: > My warning about user error was not targeted at you! :) > Sorry if it seemed so. :-) > And the order does not matter! Hm... yes you're right. But adding the disk is more prudent (or is it?) Grr. Now you've got ME thinking ! ;-) Normally, the minute a drive fails, it gets kicked and the spare would kick in and md syncs this spare. We now have a non-degraded array again. If I then fail the spare first, the array goes into degraded mode. Whereas if I hotadd the disk, it becomes a spare. Presumably if I now fail the original spare, the real disk will get synced again, to get the same setup as before. But yes, you're right; during this step it is degraded again. Oh well... > It would be cool if the rebuild to the repaired disk could be done before > the spare was failed or removed. Then the array would not be degraded at > all. Yes, but this would be impossible to do, since md cannot anticipate _which_ disk you're going to fail before it happens. ;) > If I ever re-build my system, or build a new system, I hope to use RAID6. I tried this in last fall, but it didn't work out then. See the list archives. > The Seagate test is on-line. Before I started using the Seagate tool, I > used dd. I'm not as cautious as you are. I just pray the hot spare does what its supposed to do. > My disks claim to be able to re-locate bad blocks on read error. But I am > not sure if this is correctable errors or not. If not correctable errors > are re-located, what data does the drive return? Since I don't know, I > don't use this option. I did use this option for awhile, but after > re-reading about it, I got concerned and turned it off. Afaik, if a drive senses it gets more 'difficult' than usual to read a sector, it will automatically copy it to a spare sector and reassign it. However, I doubt the OS gets any wiser this happens, so neither would md. In which cases the error gets noticed by md I don't precisely know, but I reckon that may well be when the error is uncorrectible. Not _undetectable_, to quote from another thread... 8-) > This is from the readme file: > Automatic Read Reallocation Enable (ARRE) > -Marreon/off enable/disable ARRE bit > On, drive automatically relocates bad blocks detected > during read operations. Off, drive creates Check condition > status with sense key of Medium Error if bad blocks are > detected during read operations. Hm. I would definitely ENable that option. But what do I know. It also depends I guess on how fatal reading bad data undetected is for you. For me, if one of my mpegs or mp3s develops a bad sector I can probably live with that. :-) Maarten - 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
