----- Original Message -----
From: "MRK" <mrk@xxxxxxxxxxxxx>
To: "Janos Haar" <janos.haar@xxxxxxxxxxxx>
Cc: <linux-raid@xxxxxxxxxxxxxxx>
Sent: Saturday, May 01, 2010 7:17 PM
Subject: Re: Suggestion needed for fixing RAID6
On 05/01/2010 11:37 AM, Janos Haar wrote:
Whoever, the sync_min option generally solves my problem, becasue i can
build up the missing disk from the 90% wich is good enough for me. :-)
Are you sure? How do you do that?
Resyncing a specific part is easy, replicating to a spare a specific part
is not. If the disk you want to replace was 100% made of parity data that
would be easy, you do that with a resync after replacing the disk, maybe
multiple resyncs region by region, but in your case it is not made of only
parity data. Only raid3 and 4 separate parity data from actual data, raid6
instead finely interleaves them.
If you are thinking about replacing a disk with a new one (full of zeroes)
and then resyncing manually region by region, you will destroy your data.
Because in those chunks where the new disk acts as "actual data" the
parity will be recomputed based on your newly introduced zeroes, and it
will overwrite the parity data you had on the good disks, making recovery
impossible from that point on.
You really need to do the replication to a spare as a single step, from
the beginning to the end. You cannot use sync_min and sync_max for that
purpose.
You are right again, or at least close. :-)
I have the missing sdd4 wich is 98% correctly rebuilt allready.
But you are right, because the sync_min option not works for rebuilding
disks, only for resyncing. (it is too smart to do the trick for me)
I think... unless bitmaps really do some magic in this, flagging the newly
introduced disk as more recent than parity data... but do they really do
this? people correct me if I'm wrong.
Bitmap manipulation should work.
I think i know how to do that, but the data is more important than try it on
my own.
I want to wait until somebody support this.
... or somebody have another good idea?
The general problem is, i have one single-degraded RAID6 + 2 badblock disk
inside wich have bads in different location.
The big question is how to keep the integrity or how to do the rebuild by 2
step instead of one continous?
Thanks again
Janos
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