Robert Hancock wrote:
The controller does not drop the drive from the array when it hits an
error, the 3ware card "takes care of it" and the user need not worry
about it, whereas with md/raid every time it hits a bad sector, it
breaks the raid and it goes degraded, is this correct? Will/can
something like what 3ware does be possible in a sw-raid based
configuration or is a HW raid card required?
Presumably all it's doing is writing that sector's contents back from
the other drive(s) in the array when the read error is detected, this is
something that software could do just as well. Drives only remap bad
sectors when they are written over, as a read failure doesn't
necessarily mean that the sector is entirely unreadable, but could be
due to environmental factors such as high temperature, vibration, etc.
Just rewriting the sector seems a bit questionable though, as if a drive
in your array is growing read errors that's not really a good thing..
md has done this for a while now though. If it encounters a read error in the array it will make an
attempt to write the reconstructed data back to that disk attempting to force a reallocation. I've
seen it work quite well here on disks that have the occasional grown defect.
It's certainly _much_ nicer than having the disk booted from the array on a single read error.
If the disk is haemorrhaging sectors then you will find out about it sooner or later through other
means.
Brad
--
Dolphins are so intelligent that within a few weeks they can
train Americans to stand at the edge of the pool and throw them
fish.
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