On Wed, 08 Sep 2010 05:45:41 +0000 "Michael Sallaway" <michael@xxxxxxxxxxxx> wrote: > > > -------Original Message------- > > From: Neil Brown <neilb@xxxxxxx> > > To: Michael Sallaway <michael@xxxxxxxxxxxx> > > Cc: linux-raid@xxxxxxxxxxxxxxx > > Subject: Re: 3-way mirrors > > Sent: 08 Sep '10 04:16 > > > > Interesting... will this also work for a rebuild/recovery? If so, how do I start a rebuild from a particular location? (do I just write the sync_min sector before adding the replacement drive to the array, and it will start from there when I add it?) > > > > Why would you want to? > > (My apologies for hijacking the email thread, I only meant it as a side question!) > > The reason relates to my question I posted yesterday -- I have a 12-drive raid 6 array, with 3 drives that have some bad sectors at varying locations. I planned to swap out one drive with a new one, and let it rebuild that one, then do the same for the other 2. However, when I replace and rebuild drive A, drive B gets read errors and falls out of the array (at about 50% through), but recovery continues. At the 60% mark, however, drive C gets read errors, and also falls out of the array, which now only has 9 working devices, so abandons recovery. (even though drive B has vaild data at that location, so it could be rebuilt). Hmm.... Drive B shouldn't be ejected from the array for a read error. md should calculate the data for both A and B from the other devices and then write that to A and B. If the write fails, only then should it kick B from the array. Is that what is happening? i.e. do you see messages like: read error corrected read error not correctable read error NOT corrected in the kernel logs?? If the write is failing, then you want my bad-block-log patches - only they aren't really finished yet and certainly aren't tested very well. I really should get back to those. NeilBrown > > One solution I thought of (and please, suggest others!) was to recover 55% of the array onto the new drive (A), and then stop recovery somehow. Then forcibly add drive B back into the array, and keep recovering, so that when it hits the 60% mark, even though drive C fails, it can still get parity data and recover using drive B. > > It sounds crazy, I know, but can't think of a better solution. If you have one, please suggest it! :-) > > > > You can add a new device entirely by writing to sysfs files. In this case > > you can set the 'recovery_start' for that device. This tells md that it has > > already recovered some of the array. > > Interesting, I think this is exactly what I'm after. Is this documented somewhere, or can you give me some pointers as to where to look to find more information/documentation on the sysfs files and what they do, etc.? > > Thanks! > Michael -- 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
