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

[Dilger, Andreas]

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
-- 
Andreas Dilger

Lustre Software Architect
Intel High Performance Data Division