Bad block management - which mdadm?

kernelnewbies.org reports such feature for 3.1 kernel

1.9. Software RAID: Bad block management
The MD layer (aka "Multiple Devices", aka software raid) has gained bad block management support: bad blocks will be added to a list, and the system will try not to use them. This feature requires an updated mdadm version.

Which mdadm supports that?

Arkadiusz Miśkiewicz        PLD/Linux Team
arekm / maven.pl            http://ftp.pld-linux.org/
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mdadm-3.3 will support bad block management.
However it is not released yet.

You can get current code from

git://neil.brown.name/mdadm devel-3.3

It isn't released yet because

1/ I haven't found/made time to work on mdadm and integrate support
properly.
2/ The kernel isn't really quite read for full support.

If you have a bad block list, then a write error will not fail the drive but will record the location of the write error.
This might be what you want. But if you have a hot-spare available it might not be what you want - the current kernel code will never use a hot spare until a drive fails really badly.

What it *should* do is "hot-replace". i.e. recover the data on to a spare without first removing the device with the bad block. But the hot-replace code isn't ready yet.

I expect hot-replace to be in linux-3.3 (for RAID4/5/6 at least) and I hope to release mdadm-3.3 before then with full support for bad blocks and hot replace.

For now if you use the devel-3.3 code to create a new array it will place a bad-block-log on the array and the kernel will use that bad block log to record failed blocks rather than failing the whole device.
If you want a device to be failed, you might have to explicitly do that yourself with "mdadm /dev/mdX --fail /dev/sdY"

NeilBrown