drive selection for disk arrays

Karl Denninger karl at
Sat Mar 28 00:46:23 UTC 2020

On 3/27/2020 19:39, David Christensen wrote:
> On 2020-03-27 02:45, Polytropon wrote:
>> When a drive _reports_ bad sectors, at least in the past
>> it was an indication that it already _has_ lots of them.
>> The drive's firmware will remap bad sectors to spare
>> sectors, so "no error" so far. 
> If a drive detects an error, my guess is that it will report the error
> to the OS; regardless of the outcome of a particular I/O operation
> (data read, data written, data lost) or internal actions taken (block
> marked bad, block remapped, etc.).  It is then up to the OS to decide
> what to do next.  RAID and/or ZFS offer the means for shielding the
> application from I/O and drive failures.
Yes, but...

Those drives that can do "SMART" will report (if you have a patrol
daemon for it running) if they do a "silent" sector reassignment. 
Otherwise the OS is none the wiser and neither is ZFS (or anything
else.)  Needless to say if reassignments increase you might want to
think about swapping the drive *before* it blows up!

I have the daemon running on all my machines.  It works nicely and has
warned me a few times over the years.  With that said it doesn't ALWAYS
catch a drive before it pukes.

Karl Denninger
karl at <mailto:karl at>
/The Market Ticker/
/[S/MIME encrypted email preferred]/
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