On 11/10/16 11:01, Brad Campbell wrote:

On 11/10/16 17:18, Wols Lists wrote:

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On 11/10/16 05:00, Brad Campbell wrote:

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The point is that the disk sector is not bad. So you don't want to mark
it as bad on the disk. But you know that the *data* in that block is
bad, so you want the disk access layer to fake a read error when you
try
to read it. The intent is to deliberately trigger a rewrite by md.

I suggested this a while ago. Take the badblocks log, use hdparm to mark
each bad sector as bad and put the drive back in the array. I even
suggested potentially adding a feature to ddrescue to auto-mark the
blocks as bad on the target drive.

But does that mean that the drive thinks those sectors are bad, and that
they're then lost permanently at the hardware level? That's what I
thought the badblocks list did with hdparm, and that's what I was trying
to avoid.

I've not used bad blocks list, but a cursory read would indicate it only
records a bad block if the writeback fails. That won't ever happen with
a bad sector created with hdparm. All hdparm does is corrupt the EEC on
the block so a read always returns dud. A write solves that issue nicely.

That's good to know. What happened with that suggestion for ddrescue?
Did they not like it, or was it the usual "show us the code and we'll
add it"? :-) So much to do, so little time :-)

I'm trying to build a little list of projects, partly as a result of
doing the wiki, that people wanting to get into raid programming (myself
included!) can do.

Cheers,
Wol