Re: Trouble finding bad block on WD C WD1600SB-01KBA0

On 11-Jan-2017 07:25, [email protected] wrote:
> I've also seen the UDMA_CRC_ERROR_COUNT caused by a bad SATA cable.

OK, I will make a note to look at the cable if this unit ever has 
problems like this again.  (It could have been a gamma ray or something 
hitting a gate, right?)

Now I'm trying to understand what happened here.  My best guess is that 
it went something like this (leaving out a few steps):

1.  some issue with cable, connectors, radiation etc. arose.
2.  a write to a specific block, presumably with new data, ran
     into (1) and failed.
3.  ??? the disk shuffled that data off to a temporary location
     (spare physical block, flash, or ?) and set the pending and
     UDMA_CRC_ERROR_COUNT.
4.  Read of entire disk found no errors because the disk retrieved
     either the [??? old or new] contents without problems.
5.  System was powered down for several minutes and started back up.
     The pending block and UDMA_CRC_ERROR_COUNT were still set.  
Presumably
     this means the pending data was stored in a nonvolatile location.
6.  badblocks -nvs read the bad block [??? old or new] data and then
     wrote it back to disk.  It saw no errors while doing so because
     (1) was not longer a problem.  This time the write succeeded
     and the pending block was reset to 0.  The reallocated block
     count stayed 0.  Either it didn't reallocate the block or it did and
     it didn't increment the counter.

So the question is - _which_ data is in that iffy block now?  Is it the
data which caused the failed write in the first place, or whatever was 
there
before the write?  Hopefully it is the former!

Thanks,

David Mathog
[email protected]
Manager, Sequence Analysis Facility, Biology Division, Caltech

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