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[SLUG] RAID and bad sectors


With all of the discussion about software + hardware RAID the last
week or so, I thought I'd reiterate an important lesson.

ALWAYS do a thorough sector scan before adding a drive to a RAID
array.  Adaptec's much-maligned ctrl-A utility comes in handy here:
first do a complete low level format of the drive, then do a full
verify, preferably twice.

I recently got 3 x IBM 36GB SCSI drives.  2 of which had a single
bad sector each. Not uncommon for these drives as they had originally
been set up for use on a Mac which (I guess) handles bad sector
tables differently.  Setting these up in a software RAID-5 array
caused the array to fail eventually, because as soon as a drive
is found with a bad sector it is kicked out of the array.  Needless
to say, RAID-5 doesn't handle 2 failed drives all that well.

Doing a low level format and verify using the adaptec utility
re-mapped the bad sectors, a capability inherent in the drive but
it has to be turned on by the controller.  No more problems since,
but during the process I lost about 6GB of data -- I had this
backed up off site (I'm not totally stupid) but it was a pain to
recover.

-- 
Del