Thanks for the advice.  Fortunately, the OST was completely drained of files before all heck broke loose.  With the help of the manual, a couple of lustre list threads, and some long-lost memories of a similar situation a few years back, I was able to bring the OST alive again, albeit still read-only for the time being (2 days off for me, and now I need to IO test it before I'll trust it again).


On 5/20/2014 10:49 AM, Martin Hecht wrote:
Hi bob,

just to make sure: You already followed:, especially the steps for e2fsck linked there?

If you did *not yet* do any write operation to the damaged OST, you might want to back up the whole OST first, using dd for instance (if the underlying hardware still permits it).

If the situation described (empty O directory, lost LAST_ID entry) occurred *after* the e2fsck, and you find lots of files in lost+found when you mount the OST as ldiskfs, you can use ll_recover_lost_found_objs to put them back in the correct place ( - it is part of the lustre distribution. Once I had to run this several times in order to restore the structure below.

best regards,

On 05/19/2014 08:24 PM, Bob Ball wrote:
Oh, better still, as I kept looking, and the low-level panic retreated, I found this on the mdt:

[root@lmd02 ~]# lctl get_param osc.*.prealloc_next_id

So, unless someone tells me that I am way off base, I'm going to proceed with the assumption that this is a valid starting point, and proceed to get my file system back online.


On 5/19/2014 2:05 PM, Bob Ball wrote:
Google first, ask later.  I found this in the manuals:

      26.3.4 Fixing a Bad LAST_ID on an OST

The procedures there spell out pretty well what I must do, so this should be relatively straight forward.  But, does this comment refer to just this OST, or to all OST?
*Note - *The file system must be stopped on all servers before performing this procedure.

So, is this the best approach to follow, allowing for the fact that there is nothing at all left on the OST, or is there a better short cut to choosing an appropriate LAST_ID?

Thanks again,

On 5/19/2014 1:50 PM, Bob Ball wrote:
I need to completely remake a failed OST.  I have done this in the past, but this time, the disk failed in such a way that I cannot fully get recovery information from the OST before I destroy and recreate.  In particular, I am unable to recover the LAST_ID file, but successfully retrieved the last_rcvd and CONFIGS/* files.

mount -t ldiskfs /dev/sde /mnt/ost
pushd /mnt/ost
cd O
cd 0
cp -p LAST_ID /root/reformat/sde

The O directory exists, but it is empty.  What can I do concerning this missing LAST_ID file?  I mean, I probably have something, somewhere, from some previous recovery, but that is way, way out of date.

My intent is to recreate this OST with the same index, and then put it back into production.  All files were moved off the OST before reaching this state, so nothing else needs to be recovered here.


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