[Gllug] still wondering about lvm

[Nix]

On Thu, 09 Mar 2006, Adrian McMenamin whispered secretively:
> I asked this when I recounted my tail of woe/incompetence on Sunday but
> nobody answered, so here I go again...
> 
> adrian at dragoneye:~$ sudo pvscan
>   Incorrect metadata area header checksum
>   Incorrect metadata area header checksum
>   Incorrect metadata area header checksum
>   Incorrect metadata area header checksum
>   PV /dev/sda5   VG Ubuntu   lvm2 [186.07 GB / 0    free]
>   PV /dev/hda5   VG Ubuntu   lvm2 [76.45 GB / 460.00 MB free]
>   PV /dev/hda1               lvm2 [101.76 MB]
>   Total: 3 [262.62 GB] / in use: 2 [262.52 GB] / in no VG: 1 [101.76 MB]
> 
> Firstly what does Incorrect metadata area header checksum mean and how
> can I fix it (google gives no simple/straight answers afaics and the STN
> is much better here :))

It means the metadata area's header checksum is incorrect. ;)))

FWIW, the way LVM works is that each PV has a metadata header which
gives all info on all PVs and LVs in the volume group (it's replicated
across all PVs). This header has a checksum, and it looks like that
checksum is wrong (I'd guess it's consistently wrong on each PV).


We can start getting a clue why if you run it with -vvv -dddddd and
post the results.

If all else fails there's always the lvm list, and Alasdair `LVM' Kergon
has been seen to post on the gllug list and has been seen at gllugs :)

> and if /dev/hda5 is in the Ubuntu VG why doesn't df report it:

Because VGs contain a pool of space which *may or may not* be allocated
to LVs, and those LVs *may or may not* be mounted (and may not even be
mountable: e.g. invalid snapshot volumes), and the mounted filesystems
*may or may not* be visible by the current process (although currently
most processes can see the same filesystem tree, this is not necessarily
the case).

-- 
`Come now, you should know that whenever you plan the duration of your
 unplanned downtime, you should add in padding for random management
 freakouts.'
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