On 01/02/2011 19:21, Piergiorgio Sartor wrote:
On Tue, Feb 01, 2011 at 07:52:59AM +1100, NeilBrown wrote:
On Mon, 31 Jan 2011 21:20:55 +0100 Piergiorgio Sartor
<piergiorgio.sartor@xxxxxxxx> wrote:
Hi all,
some times ago, I think was Neil, it was mentioned
about the possibility to access consistently a RAID-6
array from user space, in order to be able to perform
some checks, like the notorius "which HDD has wrong data".
Is there any reference or documentation or source code
which can be taken as example for such a case?
Look in the mdadm source code, particularly at restripe.c
Also
make test_stripe
make a program the the test suite uses for verify data correctness.
That should give you enough hints to get you started.
Hi Neil, thanks for the pointer.
I had a look at the code and there is something I did not get.
It seems to me the HDDs composing the array are "simply"
opened with "open".
In case the array is in use, how is avoided a race condition
between the "test_stripe" program and the md device?
I mean, the first could start to read from the HDDs and the
other could write something in the same place, leading to an
inconsistent parity, from the "test_stripe" point of view,
since it missed some update.
Or there is a locking inside md (in "test_stripe" I could
not see and it would also be dangerous)?
Look at Grow.c and suspend_lo and suspend_hi.
Just my €$£0.005, I may be wrong, etc.
Cheers,
John.
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