9.0.4 Data corruption issue

Hello,

Had a DB that had bloated due to lots of updates and insuffcient auto vacuum
settings. Attempted the following in the following order:

VACUUM VERBOSE full tablename;
CLUSTER tablename;

Did the full first to ensure that the cluster had enough space to run.
The db had already been previously clustered to an index. At some point
during the VACUUM I started seeing the following errors in the logs:

CONTEXT: writing block 12125253 of relation base/2651908/652397108

WARNING: could not write block 12125253 of base/2651908/652397108

DETAIL: Multiple failures --- write error might be permanent.

Also seeing the same error for block 12125253, 2978.

And the cluster failed as well. I have attempted a check point using
pg_start_backup() and that failed as well.

The system is still running and I have yet to shut it down. I am hoping to
find out what possibilities I have if any to recover from this. Also how do
I avoid this in the future?

-Ken