Is it possible to recover data after resync?

Is it possible to recover data after resync?

[Alex Davis]

Situation:

I accidentally killed the power to my 5-disk RAID 5 array. I then powered
it back up and rebooted the system. After reboot, however, I got the follow-
ing error when trying to assemble the array:

mdadm -A -amd /dev/md0 /dev/sd[a-e]
mdadm: /dev/md0 assembled from 2 drives - not enough to start the array.

I had read somewhere that it's possible to recover an array using the -C
option to mdadm. Unfortunately, I didn't specify 'missing', so instead of
recovering, it's resyncing. 

Is there any way to recover the original data?

I code, therefore I am

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Re: Is it possible to recover data after resync?

[Neil Brown]

On Wednesday July 19, alex14641@yahoo.com wrote:
> Situation:
> 
> I accidentally killed the power to my 5-disk RAID 5 array. I then powered
> it back up and rebooted the system. After reboot, however, I got the follow-
> ing error when trying to assemble the array:
> 
> mdadm -A -amd /dev/md0 /dev/sd[a-e]
> mdadm: /dev/md0 assembled from 2 drives - not enough to start the array.
> 
> I had read somewhere that it's possible to recover an array using the -C
> option to mdadm. Unfortunately, I didn't specify 'missing', so instead of
> recovering, it's resyncing. 

--assemble --force is worth try first and is much safer.

> 
> Is there any way to recover the original data?

Well, if you got all the right devices in the right order, then your
data should be fine.  If not, I hope you have good backups, because
they are your only hope.

NeilBrown

Re: Is it possible to recover data after resync?

[Alex Davis]

--- Neil Brown <neilb@suse.de> wrote:

> On Wednesday July 19, alex14641@yahoo.com wrote:
> > Situation:
> > 
> > I accidentally killed the power to my 5-disk RAID 5 array. I then powered
> > it back up and rebooted the system. After reboot, however, I got the follow-
> > ing error when trying to assemble the array:
> > 
> > mdadm -A -amd /dev/md0 /dev/sd[a-e]
> > mdadm: /dev/md0 assembled from 2 drives - not enough to start the array.
> > 
> > I had read somewhere that it's possible to recover an array using the -C
> > option to mdadm. Unfortunately, I didn't specify 'missing', so instead of
> > recovering, it's resyncing. 
> 
> --assemble --force is worth try first and is much safer.
> 
> > 
> > Is there any way to recover the original data?
> 
> Well, if you got all the right devices in the right order, then your
> data should be fine.  If not, I hope you have good backups, because
> they are your only hope.
> 
> NeilBrown
> 

So do I just keep doing mdadm -A /dev/md0 /dev/.... using different 
permutations of the devices until my data shows up?


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Re: Is it possible to recover data after resync?

[Neil Brown]

On Wednesday July 19, alex14641@yahoo.com wrote:
> > 
> > > 
> > > Is there any way to recover the original data?
> > 
> > Well, if you got all the right devices in the right order, then your
> > data should be fine.  If not, I hope you have good backups, because
> > they are your only hope.
> > 
> > NeilBrown
> > 
> 
> So do I just keep doing mdadm -A /dev/md0 /dev/.... using different 
> permutations of the devices until my data shows up?
> 

Hard to say without precise details.  Maybe it's worth a try, maybe
not.

NeilBrown

Re: Is it possible to recover data after resync?

[Alex Davis]

--- Neil Brown <neilb@suse.de> wrote:

> On Wednesday July 19, alex14641@yahoo.com wrote:
> > > 
> > > > 
> > > > Is there any way to recover the original data?
> > > 
> > > Well, if you got all the right devices in the right order, then your
> > > data should be fine.  If not, I hope you have good backups, because
> > > they are your only hope.
> > > 
> > > NeilBrown
> > > 
> > 
> > So do I just keep doing mdadm -A /dev/md0 /dev/.... using different 
> > permutations of the devices until my data shows up?
> > 
> 
> Hard to say without precise details.  Maybe it's worth a try, maybe
> not.

What details are needed?


> NeilBrown
> 


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Re: Is it possible to recover data after resync?

[Alex Davis]

--- Neil Brown <neilb@suse.de> wrote:

> On Wednesday July 19, alex14641@yahoo.com wrote:
> > > 
> > > > 
> > > > Is there any way to recover the original data?
> > > 
> > > Well, if you got all the right devices in the right order, then your
> > > data should be fine.  If not, I hope you have good backups, because
> > > they are your only hope.
> > > 
> > > NeilBrown
> > > 
> > 
> > So do I just keep doing mdadm -A /dev/md0 /dev/.... using different 
> > permutations of the devices until my data shows up?
> > 
> 
> Hard to say without precise details.  Maybe it's worth a try, maybe
> not.

Ignore my previous message. Typing 

mdadm -C -amd -l5 -n5 -c128 /dev/md0 /dev/sde /dev/sdd /dev/sdc /dev/sdb missing

seems to have done the trick. I'll do an add of /dev/sda and an fsck and report
my results later.

> NeilBrown
> 


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Re: Is it possible to recover data after resync?

[Alex Davis]

--- Alex Davis <alex14641@yahoo.com> wrote:

> 
> 
> --- Neil Brown <neilb@suse.de> wrote:
> 
> > On Wednesday July 19, alex14641@yahoo.com wrote:
> > > > 
> > > > > 
> > > > > Is there any way to recover the original data?
> > > > 
> > > > Well, if you got all the right devices in the right order, then your
> > > > data should be fine.  If not, I hope you have good backups, because
> > > > they are your only hope.
> > > > 
> > > > NeilBrown
> > > > 
> > > 
> > > So do I just keep doing mdadm -A /dev/md0 /dev/.... using different 
> > > permutations of the devices until my data shows up?
> > > 
> > 
> > Hard to say without precise details.  Maybe it's worth a try, maybe
> > not.
> 
> Ignore my previous message. Typing 
> 
> mdadm -C -amd -l5 -n5 -c128 /dev/md0 /dev/sde /dev/sdd /dev/sdc /dev/sdb missing
> 
> seems to have done the trick. I'll do an add of /dev/sda and an fsck and report
> my results later.
>

mdadm --add was successful. fsck showed no errors.

Life is good.

-Alex

I code, therefore I am

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