On 23/10/18 21:42, CygX1 wrote: > Dear all, > > I’m new to this mailing list and not actually knowledgeable with RAID > except for what I learned from the WIKI. I currently have a crashed > RAID6 volume on a Synology DS413j that I’d like to rescue. The volume > crashed due to a power failure while shutting down the DiskStation. The > original RAID had one 4 TB (/dev/sda) and three 8 TB disks (/dev/sd[bcd] > assembled in a RAID6 array. > > Now, after the crash only disk 4 (/dev/sdd3) appears to be still active, > sd[abc]3 show up as “removed”. > > The disks are almost new and I believe they are fine (no bad blocks, > etc). Re-assembling the RAID failed. So, in order to not touch the > original disks, I dd-cloned two of the drives (sdc and sdd), put them > into a Synology DS414play as sda and sdb and re-created the RAID with > > mdadm -C /dev/md2 -R -l6 -e 1.2 -n4 missing missing /dev/sda3 /dev/sdb3 > --assume-clean > > which created a new, degraded RAID6 (/dev/md2) that I hoped would bring > me my data back. Unfortunately, I still cannot mount the volume. > Synology disk station says “There is no volume in your system”. Mount > complains that it cannot read the superblock (see output below). > > Any idea how I could rescue the data and/or get the lost volume mounted > is highly appreciated. Thanks in advance. Okay. I think you've done almost everything right, but not quite ... You've still got your original disks. Great. However, I think you've just trashed your copies, so you'll need to re-copy them :-( Once you've got new copies, try putting an overlay over them, and then do an "assemble force". There's no danger of them re-sync'ing (always the risk with --force) because you've got no redundancy. But it should then put the disks back, in their correct positions in the array, with all the offsets right. The trouble (which I suspect is why your Synology can't find a superblock or anything) with re-creating an array is that the defaults have changed over time, and if you've played around at all with the disks, nothing will be in the default position anyway. So your re-creation could well have moved the disks around in the array such that what was your data-2 drive is now the P-drive etc etc. And your data may well start at offset X whereas the new default is for it to be at offset Y so the raid code is looking in the wrong place. Also etc etc... I could be wrong - I've got mostly head knowledge and not experience - but that's the first thing I would suspect. If it works with the overlays, reboot or otherwise tear it all down, and re-do it without the overlays. The point of overlaying is that you can experiment and all the changes are written to ram and not disk, so you don't trash the copies and have another frustrating X hours recreating new copies. Oh - and *do* download lsdrv, and run it over the *original* disks. Should things really go pear-shaped, that information will be invaluable. Cheers, Wol
