[linux-lvm] Meaning of LV -missing_<x>_<x> devices

[Stuart D. Gathman]

On Wed, 15 Jun 2011, Enrico Ferro wrote:

> after the extention of a logical volume (mysqld1) a new "ghost" logical 
> volume
> appeared with a <missing> suffix:
>
> brw-rw---- 1 root disk 253, 38 Feb 15 20:53 vgmysql-mysqld1
> brw-rw---- 1 root disk 253, 44 Jun 1 10:21 vgmysql-mysqld1-missing_4_0

That means the lv was extended onto a PV that is no longer online.
The missing device is the extents allocated on the missing PV.

> Before performing this LV we partitioned and added a new LUN to the existing
> vgmysql volume group (again, no errors reported).
>
> We did not discovered this strange device immediately (the lvextend
> command did not reported errors), only after resizing the file system.
> The ext2fs operation aborted and so we started with investigation.

> So online resize of the FS failed, we unmounted the LV, extended with
> (apparent) success the filesystems and lived happy for a few days. Only
> while a deep corruption of the FS appeared. :-(

You needed to do an fsck after the aborted filesystem resize.  I'm
suprised the fs resize didn't make you do so.  If you did do the fsck,
then there are serious problems with your new PV.

> A reboot cleaned up the strange "missing" LV, it is no more present.

> The point is: what is the meaning of -missing_* device? When are they
> generated (and why there are no warnings reported?)

Apparently, the new PV went offline between lvextend and resize.

--
 	      Stuart D. Gathman <stuart at bmsi.com>
     Business Management Systems Inc.  Phone: 703 591-0911 Fax: 703 591-6154
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