Re: SCSI vs. IDE performance test

Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> writes:

> I'm not at all sure what IDE drives do when they have a failure writing out
> cached buffers; anyone have experience with that?

There's a looooong discussion about this too on linux-kernel, search for
"blockbusting". I think the conclusion is "it depends".

Often write failures aren't detected until the block is subsequently read. In
that case of course there's no hope. What's worse is the drive might not remap
the block on a read, so the problem can stick around even after the error.

If the write failure is caused by a bad block and the drive detects this at
the time it's written then the drive can actually remap that block to one of
its spare blocks. This is invisible to the host.

If it runs out of spare blocks, then you're in trouble. And there's no warning
that you're running low on spare blocks in any particular region unless you
use special utilities to query the drive. Also if the failure is caused by
environmental factors like vibrations or heat then you can be in trouble too.

--
greg