From mboxrd@z Thu Jan 1 00:00:00 1970 From: Neil Brown Subject: Re: recovery problems, might be driver-related Date: Mon, 8 Feb 2010 16:52:00 +1100 Message-ID: <20100208165200.3758520a@notabene.brown> References: <4B6EC24A.9040703@stud.tu-ilmenau.de> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <4B6EC24A.9040703@stud.tu-ilmenau.de> Sender: linux-raid-owner@vger.kernel.org To: stefan.huebner@stud.tu-ilmenau.de Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids On Sun, 07 Feb 2010 14:38:18 +0100 Stefan H=C3=BCbner wrote: > Hi Everybody, >=20 > I've recently come across some RAID-Recovery problem that were kind o= f > not-so-easy-to-understand. I was trying to recover damaged RAID5s, > where one > disk died and another dropped out (most likely due to read error reco= very > timeout / not reporting back while error recovery was active) during > resync with > a spare/new disk. After taking double backups I tried to recreate th= e > raid with > the needed working disk images (to make the superblocks consistent). = During > that action mdadm told me that the last-dropped disk contained a vali= d ext3 > filesystem and was obviously part of an md-array. mdadm only checks the superblock at the start of the device to see if i= t looks like an ext3 filesystem. So if an md array has a valid filesyste= m, then it is very likely that at least one of the devices in the array wi= ll appear to have a valid filesystem to mdadm. >=20 > This happened with NAS-Devices from 2 different Vendors (namely Thecu= s and > Synology), which made me think it must be a md-raid thing. Does md-r= aid > create > a filesystem after a disk dropped out? Or may something in the syste= m > happen to > cause this strange behaviour? No, nothing would try to create a filesystem on a device just because i= t has dropped out of a RAID. >=20 > All in all: after recreating the raids the filesystem contained on it= was > totally damaged (could not even be mounted). fsck ran multiple days = with > excessive data loss. Maybe there was meant to be another layer between the md array and the filesystem - maybe LVM ?? If there should have been an LVM and wasn't = the filesystem would definitely look very corrupt even though the superbloc= k might appear to be in the right place. NeilBrown >=20 > P.S.: the mdadm-lines to recreate the RAIDs were derived from mdadm -= E - > outputs > of the original partitions, so I believe that it should have worked (= on > other > recoveries I did before it also worked well). >=20 > Does anyone have an idea what is going on there? Or may it have happ= ened - > well, I don't want to say something that could get me sued. >=20 > All the best, > Stefan H=C3=BCbner > -- > To unsubscribe from this list: send the line "unsubscribe linux-raid"= in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-raid" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html