Is it possible to read a corrupted Sequence File?

[Hs <as...@gmail.com>]

Hi,

I am running hadoop 1.0.3 and hbase-0.94.0on a 12-node cluster. For unknown
operational faults, 6 datanodes  have suffered a complete data loss(hdfs
data directory gone).  When I restart hadoop, it reports "*The ratio of
reported blocks 0.8252*".

I have a folder in hdfs containing many important files in hadoop
SequenceFile format. The hadoop fsck tool shows that  (in this folder)

Total size:    134867556461 B
 Total dirs:    16
 Total files:   251
 Total blocks (validated):      2136 (avg. block size 63140241 B)
  ********************************
  CORRUPT FILES:        167
  MISSING BLOCKS:       405
  MISSING SIZE:         25819446263 B
  CORRUPT BLOCKS:       405
  ********************************

I wonder if I can read these corrupted SequenceFiles with missing blocks
skipped ?  Or, what else can I do now to recover these SequenceFiles as
much as possible ?

Please save me.

Thanks !

Re: Is it possible to read a corrupted Sequence File?

[Radim Kolar <hs...@filez.com>]

also if you will be seek an expert help disconnect drives with 
disappearing data, they will be still there in good shape as long they 
are not overwritten. and of course do not delete any fsimage from name node.

Re: Is it possible to read a corrupted Sequence File?

[Radim Kolar <hs...@filez.com>]

> Could you please provide a little more detail?
Its low level task, repairing seq files with header missing is not so 
easy. But till date we were able to repair pretty much everything people 
needed including corrupted hbase metadata. But its few days of work, 
which is far beyond you can get for free in community mailing list.
> Should I run "hadoop fsck -move " first to move broken files into /lost+found and then repair
> them?
no, it does more harm then good. Best advice is never try to do any data 
recovery yourself and seek an expert.

But if cost of expert work is more then cost of data, then yes why not 
to try it? I never used that myself, but you probably do not have much 
other choices.

Re: Is it possible to read a corrupted Sequence File?

[Hs <as...@gmail.com>]

Could you please provide a little more detail?  Should I run "hadoop fsck
 / -move " first to move broken files into /lost+found and then repair
them? Or, I can repair them directly in current path?
Thanks!


2012/11/24 Radim Kolar <hs...@filez.com>

>
>  I wonder if I can read these corrupted SequenceFiles with missing blocks
>> skipped ?
>>
> Its possible to recover existing blocks and repair seq file structure.
>

Re: Is it possible to read a corrupted Sequence File?

[Radim Kolar <hs...@filez.com>]

> I wonder if I can read these corrupted SequenceFiles with missing blocks
> skipped ?
Its possible to recover existing blocks and repair seq file structure.