[dm-devel] Activate/rebuilding with broken disk

Mitura, Radoslaw radoslaw.mitura at intel.com
Mon Feb 11 22:11:01 UTC 2008


Hi,

I'm writing code to make data recovery (rebuild) with
dmraid/device-mapper.
Assume I have created and mounted a mirror raid volume with disk A and
B.
# dmsetup table
isw_dgdccjfdbi_test: 0 20971779 mirror core 2 16384 nosync 2 8:16 0 8:32
0 1 handle_errors
# dmsetup status
isw_dgdccjfdbi_test: 0 20971779 mirror 2 8:16 8:32 1281/1281 1 AA 1 core

When I remove one of disk (assume A) and make write or read from that
volume I receive dmsetup status with one "AD" (with appropriate patches
to kernel).
I can work with one broken disk (assume it is mirror) and device-mapper
will take care of next writes/reads to be directed only to device B.
Then I add a new disk C (for example 8:48).

Some questions I have:
1. How to update device mapper table in a way where device-mapper will
know that I have only disk B and C and that C is a new empty disk that
should not be used at the moment?
2. If 1 is possible without interrupting system work (volume is still
mounted) then is it possible to start rebuilding of disk B to C (also
with mounted volume)?
3. During rebuild "dmsetup status" will show rebuild progress from
0//1281 to 1281/1281 - assume it is in the middle 500/1281
A) Does device mapper take care of writes to disk B and C together if
they are directed to blocks just recovered?
B) Does device mapper take care of writes only to disk B if they are
directed to blocks not recovered yet?

Regards,
Radoslaw Mitura


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