On Wed, 13 Oct 2010 00:59:52 +0200 Simon SÃHIER <simon@xxxxxxxxx> wrote: > On 12 oct. 2010 22:46:12, Neil Brown wrote : > > On Tue, 12 Oct 2010 16:27:53 +0200 > > > > Simon S <simon@xxxxxxxxx> wrote: > > > Hi all, > > > > > > I had a config with 5 disks and 3 raid 5 arrays: > > > > > > md2 : system root > > > md3 : swap > > > md4 : data > > > > > > I added a 6th disk with the intention of growing my raid5 into raid6. > > > > > > The step I used were : > > > > > > # mdadm /dev/mdX -a /dev/newdiskX > > > # mdadm -G --level 6 -n 6 /dev/mdX --backup-file /mdXbackup > > > > > > (yes, with backup file on root partition md2...) > > > > Bad idea.. Very bad idea. > > > > > The md3 array reshaped without any problem. > > > md2 seemed to reshape well until it reaches 50.4%, then the rebuild speed > > > stalled at 14Kb/s. > > > > This is the expected consequence of that bad idea. Unfortunately it would > > be hard to reliably get mdadm to complain about that, though I guess the > > common cases are easy to protect against ... added to 'todo' list > > > > > md4 was still in the state "resync=DELAYED" then. > > > > > > As the rebuild process seemed hung, I restart the machine ... bad idea. > > > > Not really, nothing else would have worked. > > > > > Now mdadm refuses to assemble md2 and md4, and displays this message : > > > mdadm: Failed to restore critical section for reshape, sorry. > > > > > > Possibly you needed to specify the --backup-file > > > > > > md2 is my linux installation, not very bad if I lose this one. > > > > > > md4 however contains valuable data. > > > > > > While md4 was still in the state resync=DELAYED before the shutdown, I > > > expect it should not has been (to much) modified and can be recovered. > > > > Very true. > > > > > Any idea on how I could safely do it ? > > > > > > Should I give a try to the hack "Get 'Grow_restart' to always return 0." > > > mentionned by Neil Brown on 22 april 2010 in this mailing list ? > > > > That is your best bet. I plan to make that easier to do in mdadm-3.2 (no > > recompile necessary). > > > > Before you do, check "mdadm -E /dev/newdiskX" and make sure the "Reshape > > position" is 0. If it is you should be fine. I > > > > It won't be for md2 of course. So md will quite possible have some > > corruption. Run fsck on it an it will probably be mostly OK, but there is > > a reasonable chance that some files will be corrupted. Whether and when > > you will notice is impossible to guess. > > Thanks for your answer Neil, > > I recompiled mdadm 3.1.4 with return 0 in the beginning of the function > Grow_restart (mistake was made with 3.1.2). I have one more question : > > I first tried assembling the least valued array, md2. It starts reshaping from > where it stops, in the first seconds around 1300 K/s, and rapidly above 10K/s. > > While my backup file for md4 (the array I care about) was also on md2. Do I > have to expect a problem assembling md4 with the modified version of mdadm, or > can I go without worying md2 (rootfs) isn't assembled ? The backup file for md4 would have been essentially empty. It can be created anew elsewhere. I probably wouldn't rick using the original backup file even if you can access it, as it could be corrupted. So when you assemble md4, give it a fresh backup file in some stable location, and use the hacked mdadm. NeilBrown > > > > > > NeilBrown > > > > > Thank for any advices, > > > > > > Cheers, > > > > -- > > 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
