Am 07.03.2007 um 16:14 schrieb Bill Davidsen:
Neil Brown wrote:
On Monday March 5, ralf@xxxxxxxx wrote:
Is it possible to mark a disk as "to be replaced by an existing
spare",
then migrate to the spare disk and kick the old disk _after_
migration
has been done? Or not even kick - but mark as new spare.
No, this is not possible yet.
I was thinking about this, and looked at the code a bit.
[ ... ]
What I was thinking is to trigger the code to rebuild on spare, but
to only rebuild the data from parity of the drive being replaced
were unreadable.
Sounds good to me ...
That should make the process run much faster. any write would
present a different problem, I would say the data would go to the
new drive, and if bitmap was enabled the bit would be set for the
old drive but no write done.
But then you need to copy the whole block that is covered by a bit in
the bitmap to the new drive on every write that is done to the raid -
am I
right? For small random writes this could be a real performance hit.
If the new drive failed during the migrate the old drive could then
be resynced. Without a bitmap you DO want to write the old drive if
it's good, DON'T if you think it's failing.
Without a bitmap I would suggest to try to write to the old _and_ the
new drive.
In case of a write error on the old drive it seems best to me to not
kick
it - as it would be done normally - but ignore the error and hope the
next time
one tries to write this sector it is still not writable (just in case
we have to
stop migration for any reason). Or is there any way to mark a sector
as invalid
on a raid without bitmap?
In case the new drive fails it should be kicked as usual ...
Ok ... for not having any idea what the raid code actually does this was
quite a lot of text ... hopefully it was not only noise.
Ralf
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