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Re: [linux-lvm] Simulating LVM Mirror Failure and recovery



Tomasz Chmielewski wrote:
vu pham schrieb:

as per the redhat guide this should result in mirror leg failure and any subsequent write activity to the mirror should convert the mirror into linear volume. but the output of lvs command still shows copy % as 100%. also data in filesystem of lv1 is erased and it is converted into read only filesystem.

can anyone please let us know the correct way to simulate lvm mirror failure and recovery.

thanks and regards

I think to simulate error failure you have to write to the underlying devices, not the mirrored device. When you write to the mirrored device, lvl1 in this case, data is mirrored so there is no failure at all. So I think you have to dd to either /dev/sda3 or /dev/sdb3.

How will LVM distinguish between a valid and invalid copy in that case?

Are you sure that on reads, LVM will return data from the "good" copy, not the one you just overwrote with "dd if=/dev/zero of=/dev/sdb seek=xxx bs=1M count=10"?

Good question. I thought that dd will destroy the lvm information at the beginning of the partition which makes the leg broken. I made the following test and the result is odd:

- created mirrored logical volumn mrlv1 on /dev/sdc1 and /dev/sdd1, having /dev/sdd2 as log device
- mkfs.ext3 /dev/vg1/mrlv1, mount it and copy files onto it.
- dd if=/dev/zero of=/dev/sdd1
- read / write onto the mounted mirror lvm.

The output of lvs  shows:
- lvm information on /dev/sdd2 is destroyed
- the 2nd mirror, which is /dev/sdd2, is *unknown device*
- the mirror is still ok

And no lvm log in /var/log/messages.

[root xen3 ~]# lvs -a -o +devices
  Couldn't find device with uuid 'ZUOCeZ-Ssb2-0fP6-n5YY-sz5n-TtXe-b7eL3a'.
  Couldn't find device with uuid 'ZUOCeZ-Ssb2-0fP6-n5YY-sz5n-TtXe-b7eL3a'.
  Couldn't find device with uuid 'ZUOCeZ-Ssb2-0fP6-n5YY-sz5n-TtXe-b7eL3a'.
  Couldn't find device with uuid 'ZUOCeZ-Ssb2-0fP6-n5YY-sz5n-TtXe-b7eL3a'.
  Couldn't find device with uuid 'ZUOCeZ-Ssb2-0fP6-n5YY-sz5n-TtXe-b7eL3a'.
  Couldn't find device with uuid 'ZUOCeZ-Ssb2-0fP6-n5YY-sz5n-TtXe-b7eL3a'.
  Couldn't find device with uuid 'ZUOCeZ-Ssb2-0fP6-n5YY-sz5n-TtXe-b7eL3a'.
  LV               VG   Attr   LSize   Origin Snap%  Move Log
[... deleted unrelated devices ...]

mrlv1 vg1 mwi-ao 200.00M mrlv1_mlog 100.00 mrlv1_mimage_0(0),mrlv1_mimage_1(0) [mrlv1_mimage_0] vg1 iwi-ao 200.00M /dev/sdc1(0) [mrlv1_mimage_1] vg1 iwi-ao 200.00M unknown device(0) [mrlv1_mlog] vg1 lwi-ao 4.00M /dev/sdd2(0)



Vu


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