On 14/10/15 01:42, Adam Goryachev wrote:
On 14/10/15 05:09, Benjamin ESTRABAUD wrote:
Hi Marek,
On 13/10/15 16:04, Marek wrote:
Could it be that the raid wasnt synced at the time i overwrote
/dev/sda ? i have run the command you suggested and will report after
its done. would it still be possible to recover the raid?
So what likely happened is that you wrote ontop of a RAID member drive
while the RAID was likely not assembled (during your install).
If you do a resync it won't unfortunately *recover* the previously
written data, it will go over each stripe and recalculate the parity.
It is true that it *might* have been possible to do the opposite
operation by not touching anything and figuring out the previous data
with the data and parity blocks from the remaining RAID members
(assuming they weren't overwritten), but it would have been a tricky
operation. However, since you've done the resync now, the previous
parity blocks have been overwritten leaving you with a consistent
RAID, but with part of the data on a disk that you want to revert.
Or better action would be to stop the array, start the array excluding
sda (not sure best way to manually mark it failed, or maybe physically
remove it, or zero superblock should work too). Then you should have
clean degraded array with all data. Now you could add sda back, and it
will re-write correct data. (Assuming no writes were done to sdb/sdc/sdd).
I agree with Adam, in this particular case the data would be recovered
on "sda". Doing a plain and simple resync with the array not degraded
would do another operation which is precisely what you don't want, i.e.
make sure that the parity are recalculated from the current data.
Depending on what you actually did, and what order, it might still work....
If the resync didn't run while sda was in the array it should, otherwise
the data recalculated on sda will be identical to the current data.
Regards,
Adam
At this stage you should recover the old data from a backup.
On Tue, Oct 13, 2015 at 4:36 PM, Weedy <weedy2887@xxxxxxxxx> wrote:
On 13 Oct 2015 10:06 am, "Marek" <mlf.conv@xxxxxxxxx> wrote:
no, i had a working raid consisting of 4 2TB drives (raid5)
sda,sdb,sdc,sdb ( no partitions were created on drives) - then i
accidentally deleted /dev/sda by installing ubuntu. when inspecting
dev/md127 with a hex editor i discovered first 12mb are missing.
Wait, if it's a raid5 can't you just resync it?
Also I believe 1.2 metadata is at the end of a partition. If your
saying the
raids hasn't noticed you can run a check and it should fix itself.
echo check > /sys/block/mdX/md/sync_action
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