[ceph-users] Recover files from cephfs data pool

Sergey Malinin hell at newmail.com
Mon Nov 5 17:10:40 PST 2018


With cppool you got bunch of useless zero-sized objects because unlike "export", cppool does not copy omap data which actually holds all the inodes info.
I suggest truncating journals only for an effort of reducing downtime followed by immediate backup of available files to a fresh fs. After resetting journals the part of your fs covered by not flushed "UPDATE" entries *will* become inconsistent. MDS may start to occasionally segfault but it can be avoided by setting forced readonly mode (in this mode MDS journal will not flush so you will need extra disk space).
If you want to get the original fs recovered and fully functional - you need to somehow replay the journal (I'm unsure whether cephfs-data-scan tool operates on journal entries).



> On 6.11.2018, at 03:43, Rhian Resnick <xantho at sepiidae.com> wrote:
> 
> Workload is mixed. 
> 
> We ran a rados cpool to backup the metadata pool. 
> 
> So your thinking that truncating journal and purge queue (we are luminous) with a reset could bring us online missing just data from that day. (most when the issue started)
> 
> If so we could continue our scan into our recovery partition and give it a try tomorrow after discussions with our recovery team. 
> 
> 
> 
> 
> On Mon, Nov 5, 2018 at 7:40 PM Sergey Malinin <hell at newmail.com <mailto:hell at newmail.com>> wrote:
> What was your recent workload? There are chances not to lose much if it was mostly read ops. If such, you must backup your metadata pool via "rados export" in order to preserve omap data, then try truncating journals (along with purge queue if supported by your ceph version), wiping session table, and resetting the fs.
> 
> 
>> On 6.11.2018, at 03:26, Rhian Resnick <xantho at sepiidae.com <mailto:xantho at sepiidae.com>> wrote:
>> 
>> That was our original plan. So we migrated to bigger disks and have space but recover dentry uses up all our memory (128 GB) and crashes out. 
>> 
>> On Mon, Nov 5, 2018 at 7:23 PM Sergey Malinin <hell at newmail.com <mailto:hell at newmail.com>> wrote:
>> I had the same problem with multi-mds. I solved it by freeing up a little space on OSDs, doing "recover dentries", truncating the journal, and then "fs reset". After that I was able to revert to single-active MDS and kept on running for a year until it failed on 13.2.2 upgrade :))
>> 
>> 
>>> On 6.11.2018, at 03:18, Rhian Resnick <xantho at sepiidae.com <mailto:xantho at sepiidae.com>> wrote:
>>> 
>>> Our metadata pool went from 700 MB to 1 TB in size in a few hours. Used all space on OSD and now 2 ranks report damage. The recovery tools on the journal fail as they run out of memory leaving us with the option of truncating the journal and loosing data or recovering using the scan tools. 
>>> 
>>> Any ideas on solutions are welcome. I posted all the logs and and cluster design previously but am happy to do so again. We are not desperate but we are hurting with this long downtime. 
>>> 
>>> On Mon, Nov 5, 2018 at 7:05 PM Sergey Malinin <hell at newmail.com <mailto:hell at newmail.com>> wrote:
>>> What kind of damage have you had? Maybe it is worth trying to get MDS to start and backup valuable data instead of doing long running recovery?
>>> 
>>> 
>>>> On 6.11.2018, at 02:59, Rhian Resnick <xantho at sepiidae.com <mailto:xantho at sepiidae.com>> wrote:
>>>> 
>>>> Sounds like I get to have some fun tonight. 
>>>> 
>>>> On Mon, Nov 5, 2018, 6:39 PM Sergey Malinin <hell at newmail.com <mailto:hell at newmail.com> wrote:
>>>> inode linkage (i.e. folder hierarchy) and file names are stored in omap data of objects in metadata pool. You can write a script that would traverse through all the metadata pool to find out file names correspond to objects in data pool and fetch required files via 'rados get' command.
>>>> 
>>>> > On 6.11.2018, at 02:26, Sergey Malinin <hell at newmail.com <mailto:hell at newmail.com>> wrote:
>>>> > 
>>>> > Yes, 'rados -h'.
>>>> > 
>>>> > 
>>>> >> On 6.11.2018, at 02:25, Rhian Resnick <xantho at sepiidae.com <mailto:xantho at sepiidae.com>> wrote:
>>>> >> 
>>>> >> Does a tool exist to recover files from a cephfs data partition? We are rebuilding metadata but have a user who needs data asap.
>>>> >> _______________________________________________
>>>> >> ceph-users mailing list
>>>> >> ceph-users at lists.ceph.com <mailto:ceph-users at lists.ceph.com>
>>>> >> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com <http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com>
>>>> > 
>>>> 
>>> 
>> 
> 

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