Re: Using the new bad-block-log in md for Linux 3.1

[Lutz Vieweg <lvml@5t9.de>]

On 07/27/2011 06:16 AM, NeilBrown wrote:
> Then as errors occur they will cause the faulty block to be added to the log rather
> than the device to be remove from the array.

Can you describe the criteria for MD considering a block as faulty?

In your blog, I read
  "... known to be bad. i.e. either a read or a write has recently failed..."
but that definition may be problematic: I've experienced drives
with intermittent read / write failures (due to controller or power stability
problems), and I wonder whether such a situation could quickly fill up the
"bad block list", doing more harm than good in the "intermittent error"-
szenario.

Another szenario: The write succeeded, but a later reads of the same
block return read errors. This would result in a "pending sector", and the
harddisk may very well re-map the sector on the next write. Do you mark
the block faulty on the MD level after the first read failed (even though
subsequent reads/writes to the block would succeed), or do you first try
to re-write the block, and call it faulty only if that fails?

One more general thing: I guess that "marking bad blocks" is probably
unsuitable for SSDs, which usually do not assign fixed physical
storage location with a certain block number. Maybe mdadm could warn about better
not enabling the feature if the device is known to be a SSD.


Regards,

Lutz Vieweg