Re: Data recovery

[Wols Lists <antlists@youngman.org.uk>]

On 21/09/17 01:08, Vojtěch Kletečka wrote:
> Dear linux-raid subscribers,
> 
> may I humbly request your assistance?
> 
> I have three disks connected over usb from which I have made raid10
> array with two far coppies. Ocasionally when connecting all three
> disks to another computer one or two of the disks are not visible when
> creating array due to bad contacts on usb port. Sometimes also one of
> the disks suddenly disconnects from the array.

Why are they connected over USB?

> So far I always managed to solve the problems caused by these (very
> poor, I am fully aware of that now) conditions by readding disk and
> letting it synchronize with other disks. But now I apparently caused a
> bigger issue because I am not able to assemble the raid at all.
> 
Raid doesn't like USB. Because USB likes dropping disks and then raid
wonders where the disk has gone - sounds exactly like what's happened to
you!

> As far as I remember when I connected the disks today, linux detected
> only one. After few tries I found right usb ports for all three disks
> and they were indeed shown in output of fdisk -l. But device was not
> assembled at first. I have waited a little bit and mdadm finally
> assembled the device (although I am not sure if there were two or
> three devices). Strangely "cat /proc/mdstat" reported that devices are
> 99.something synchronized but supposedly with all blocks synchronized
> (I mean both numbers were exactly the same) and 0kb speed. Weird I
> thought and I issued mdadm --stop /dev/md127 because I wasn't able to
> mount /dev/md127 to filesystem.
> 
> That was last thing I was able to do with the array. After that I have
> tried all possible combinations of disks, assembling and incremental
> assembling with/without --force and/or --run but everything without
> any results. All commands just failed, in most cases with these two
> errors:
> 
> sudo mdadm --assemble /dev/md127 /dev/sd[cde]1
> mdadm: /dev/md127 assembled from 2 drives - need all 3 to start it
> (use --run to insist).
> (this command caused "kicking non-fresh sdd1 from array!" in dmesg)
> 
> sudo mdadm --assemble /dev/md127 /dev/sd[cde]1 --run
> mdadm: failed to RUN_ARRAY /dev/md127: Input/output error
> (this command caused "not enough operational mirrors." in dmesg)
> 
> From various examining commands (see archive for all commands
> requested in "asking for help" part of wiki here:
> http://mysharegadget.com/328200519) I have concluded, that one of
> disks is far behind others in synchronization and other two disks
> strangely don't have enough mirrors (although I though there are
> exactly two disks where each block of data is written, at least in
> this case).
> 
> sudo mdadm --examine /dev/sd[c-e]1 | egrep 'Event|/dev/sd'
> /dev/sdc1:
>          Events : 44607
> /dev/sdd1:
>          Events : 36570
> /dev/sde1:
>          Events : 44607
> 
> Is there any possibility of data recovery? For example by forcing
> mdamd to think that the disks are synchronized?

This looks good for data recovery ...

> As far as I know the disks should be synchronized because last time my
> brother used the array he let it synchronize afterwards. Also I
> haven't used "mdadm --create" yet as it might be dangerous and I am
> not sure if all data saved in array are backed up.

Thank $DEITY for that - do NOT use --create - at least don't use it if
you want to recover your data !!!
> 
> Thank you for your time and any suggestions.
> 
Get a SATA add in card if you don't have enough SATA ports, and get rid
of USB !!!

I'll let others chime in on how to get your array back - IF you put the
drives on SATA, I hope it's just a simple "--assemble --force" which
will result in everything sorting itself out, but we'll see. But don't
put USB drives into a raid array!

> With kind regards,
> 
> Vojtěch Kletečka

Cheers,
Wol