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[dm-devel] Activate/rebuilding with broken disk

Title: Activate/rebuilding with broken disk


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?

Radoslaw Mitura

Intel Technology Poland sp. z o.o.
z siedziba w Gdansku
ul. Slowackiego 173
80-298 Gdansk

Sad Rejonowy Gdansk Polnoc w Gdansku, 
VII Wydzial Gospodarczy Krajowego Rejestru Sadowego, 
numer KRS 101882

NIP 957-07-52-316
Kapital zakladowy 200.000 zl

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