[lustre-discuss] [HPDD-discuss] possible to read orphan ost objects on live filesystem?

[Chris Hunter]

Hi Andreas,
Thanks for your help.

If you have a striped lustre file with "holes" (ie. one chunk is gone 
due hardware failure, etc.) are the remaining file chunks considered 
orphan objects ?

AFAIK the online lfsck tool will scrub orphan objects. When mounting a 
OST on our oss server, I see syslog messages such as:
> Aug 31 23:20:45 oss1 kernel: Lustre: test-OST0002: deleting orphan objects from 0x0:228989008 to 0x0:228989127

Which leads me to believe these OST objects are subject to removal. 
However I don't know what exactly are orphan objects.

thanks,
chris hunter
chris.hunter at yale.edu

On 09/01/2015 12:58 AM, Dilger, Andreas wrote:
> On 2015/08/31, 3:46 PM, "HPDD-discuss on behalf of Chris Hunter"
> <hpdd-discuss-bounces at lists.01.org on behalf of chris.hunter at yale.edu>
> wrote:
>
>> I am recovering from lustre OST failure and subsequent file corruption.
>> We have striped files each with 1 missing chunk. I would like to dump
>> the remaining file chunks from the OST. We have some tools (eg. debugfs)
>> to grab the good chunks.
>>
>> My question, if we put the filesystem into production (ie. users start
>> writing new files). What will happen to these good chunks ?
>>
>> Does lustre consider these "orphan" inodes (and lfsck deletes them) ?
>
> Since it was the OST that failed and not the MDT, then the remaining OST
> objects would not be removed.
>
> You can read the good chunks of such a file using:
>
>    dd if=<file> of=<file>.new bs=1M conv=sync,noerror count=<size_in_mb>
>    truncate --size=<size_in_bytes> <file>.new
>
> The "conv=sync,noerror" allows reading from the file without failing
> for the read errors returned from the missing stripe.  However, this
> also prevents the dd from stopping when it hits the end of file, so
> the number of chunks to be read needs to be specified.
>
> Cheers, Andreas
>