[linux-lvm] 64K limit for VG/LV

[linux-lvm] 64K limit for VG/LV

[Dieter Stueken]

I just merged two volume groups without any error message,
but the result seems to have more than 65535 LE now. The only
effect until now is, that the number of free PE becomes negative
and is displayed as an unsigned huge value:

--- Volume group ---
VG Name               vg0
VG Access             read/write
VG Status             available/resizable
VG #                  0
MAX LV                256
Cur LV                9
Open LV               2
MAX LV Size           255.99 GB
Max PV                256
Cur PV                4
Act PV                4
VG Size               286.33 GB
PE Size               4.00 MB
Total PE              73300
Alloc PE / Size       97200 / 379.69 GB
Free  PE / Size       4294943396 / 1.91 TB
VG UUID               QDKBpV-xwqr-gO3b-VKiA-Jaf4-grmm-pWEY32

My VG consists of 4 x 75 GB IBM-DTLA-307075. Should I worry now?
If there is any limit of 65536 I might suspect some 16bit value
for PE addressing. If no overflow is checked, a wrong PE may be
addressed beyond LE 65536 and my VG possibly gets destroyed :-(

But I found some hints in the mailing archive, saying that the
64K limit does not affect the VG itself but only each LV inside.
Thus as long as each of my LV is <256G I don't have to worry, and
the reported "Free PE" might be just cosmetics.

Besides, vgdisplay says: "Logical Volume Manager 1.0.1-rc2"
On SuSE 7.3 running 2.4.16.

If I want to increase my LE size, I think I have to create a new VG.
Is there any tool to copy my LVs to the new VG other than "dd"?

Dieter.
-- 
Dieter St�ken, con terra GmbH, M�nster
    stueken@conterra.de         stueken@qgp.uni-muenster.de
    http://www.conterra.de/     http://qgp.uni-muenster.de/~stueken
    (0)251-980-2027             (0)251-83-334974

Re: [linux-lvm] 64K limit for VG/LV

[Heinz J . Mauelshagen]

On Tue, Jan 22, 2002 at 01:57:51PM +0100, Dieter Stueken wrote:
> I just merged two volume groups without any error message,
> but the result seems to have more than 65535 LE now. The only
> effect until now is, that the number of free PE becomes negative
> and is displayed as an unsigned huge value:
> 
> --- Volume group ---
> VG Name               vg0
> VG Access             read/write
> VG Status             available/resizable
> VG #                  0
> MAX LV                256
> Cur LV                9
> Open LV               2
> MAX LV Size           255.99 GB
> Max PV                256
> Cur PV                4
> Act PV                4
> VG Size               286.33 GB
> PE Size               4.00 MB
> Total PE              73300
> Alloc PE / Size       97200 / 379.69 GB
> Free  PE / Size       4294943396 / 1.91 TB
> VG UUID               QDKBpV-xwqr-gO3b-VKiA-Jaf4-grmm-pWEY32
> 
> My VG consists of 4 x 75 GB IBM-DTLA-307075. Should I worry now?
> If there is any limit of 65536 I might suspect some 16bit value
> for PE addressing. If no overflow is checked, a wrong PE may be
> addressed beyond LE 65536 and my VG possibly gets destroyed :-(
> 
> But I found some hints in the mailing archive, saying that the
> 64K limit does not affect the VG itself but only each LV inside.

Dieter,
that's correct. It is just a per LV limit for the max amount of its
Logical Extents (LEs).

> Thus as long as each of my LV is <256G I don't have to worry, and
> the reported "Free PE" might be just cosmetics.

Cosmetics is a nice way to put it :-)
We probably have missed that one, because for a VG with such a large capacity
we choosed larger PE sizes.

> 
> Besides, vgdisplay says: "Logical Volume Manager 1.0.1-rc2"
> On SuSE 7.3 running 2.4.16.
> 
> If I want to increase my LE size, I think I have to create a new VG.
> Is there any tool to copy my LVs to the new VG other than "dd"?

cat ;-)
No, sorry. None included in LVM.

> 
> Dieter.
> -- 
> Dieter Stüken, con terra GmbH, Münster
>     stueken@conterra.de         stueken@qgp.uni-muenster.de
>     http://www.conterra.de/     http://qgp.uni-muenster.de/~stueken
>     (0)251-980-2027             (0)251-83-334974
> 
> _______________________________________________
> linux-lvm mailing list
> linux-lvm@sistina.com
> http://lists.sistina.com/mailman/listinfo/linux-lvm
> read the LVM HOW-TO at http://www.sistina.com/lvm/Pages/howto.html

-- 

Regards,
Heinz    -- The LVM Guy --

*** Software bugs are stupid.
    Nevertheless it needs not so stupid people to solve them ***

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-

Heinz Mauelshagen                                 Sistina Software Inc.
Senior Consultant/Developer                       Am Sonnenhang 11
                                                  56242 Marienrachdorf
                                                  Germany
Mauelshagen@Sistina.com                           +49 2626 141200
                                                       FAX 924446
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-

Re: [linux-lvm] 64K limit for VG/LV

[Dieter Stueken]

"Heinz J . Mauelshagen" schrieb:
> that's correct. It is just a per LV limit for the max amount of its
> Logical Extents (LEs).
> 
> > Thus as long as each of my LV is <256G I don't have to worry, and
> > the reported "Free PE" might be just cosmetics.
> 
> Cosmetics is a nice way to put it :-)
> We probably have missed that one, because for a VG with such a large capacity
> we choosed larger PE sizes.

but I still worry a bit about my data. The reason for the wrong "Free 
PE"
reported seems not to be the 64k limit, but the fact that some of my LVs
are reported/counted twice!

-> vgdisplay -v vg0  | fgrep "LV Name"
LV Name                /dev/vg0/root
LV Name                /dev/vg0/win2k
LV Name                /dev/vg0/ortho
LV Name                /dev/vg0/praktikum
LV Name                /dev/vg0/swap
LV Name                /dev/vg0/mirror
LV Name                /dev/vg0/disk_huetti
LV Name                /dev/vg0/SuSE-7.3
LV Name                /dev/vg0/mirror          <<<<<
LV Name                /dev/vg0/disk_huetti     <<<<<

Thus I still fear of some evil inconsistencies for my data.
Is there any tool available like "e2fsck" for LVM to resolve such a
problem?

Dieter.