[linux-lvm] Pvmove question

[linux-lvm] Pvmove question

[Jean-Eric Cuendet]

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Hi,
I have a pvmove question:
In the man page, it's said to be careful with pvmove if you use it while
LVM is in use.
I don't really understand what is dangerous and what is safe...

Could you give me details? Is it safe to do if no LV is mounted? Or if
vgchange -an is run?

Thanks for any help.
-jec

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Jean-Eric Cuendet
Linkvest SA
Av des Baumettes 19, 1020 Renens Switzerland
Tel +41 21 632 9043  Fax +41 21 632 9090
http://www.linkvest.com  E-mail: jean-eric.cuendet@linkvest.com
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Re: [linux-lvm] Pvmove question

[Joe Thornber]

On Fri, Aug 24, 2001 at 12:31:18AM +0200, Jean-Eric Cuendet wrote:
> 
> Hi,
> I have a pvmove question:
> In the man page, it's said to be careful with pvmove if you use it while
> LVM is in use.
> I don't really understand what is dangerous and what is safe...

pvmove on a mounted (or otherwise in use) LV might cause curruption of
your data.

> 
> Could you give me details? Is it safe to do if no LV is mounted?

y

 Or if
> vgchange -an is run?

y

- Joe

Re: [linux-lvm] Pvmove question

[Kevin M Corry]

> On Fri, Aug 24, 2001 at 12:31:18AM +0200, Jean-Eric Cuendet wrote:
> >
> > Hi,
> > I have a pvmove question:
> > In the man page, it's said to be careful with pvmove if you use it
while
> > LVM is in use.
> > I don't really understand what is dangerous and what is safe...
>
> pvmove on a mounted (or otherwise in use) LV might cause curruption of
> your data.

In what cases could pvmove cause corruption on a mounted LV? Looking
at the man page and scanning through pvmove.c, it seems to indicate
that only a system crash during pvmove would corrupt the data. Is
this the only case, or are there others?

If there are other possibilities for corruption, wouldn't it be a
good idea to not allow pvmove's on PV's that contain mounted LVs?
You can figure out all of the LVs that are contained within a PV
using the PE map, and there are a variety of ways in user-space to
determine if a device is mounted (/proc/mounts probably being the
easiest).

> >
> > Could you give me details? Is it safe to do if no LV is mounted?
>
> y
>
> >  Or if
> > vgchange -an is run?
>
> y
>
> - Joe


-Kevin

Re: [linux-lvm] Pvmove question

[Joe Thornber]

On Mon, Aug 27, 2001 at 08:46:33AM -0500, Kevin M Corry wrote:
> > On Fri, Aug 24, 2001 at 12:31:18AM +0200, Jean-Eric Cuendet wrote:
> > >
> > > Hi,
> > > I have a pvmove question:
> > > In the man page, it's said to be careful with pvmove if you use it
> while
> > > LVM is in use.
> > > I don't really understand what is dangerous and what is safe...
> >
> > pvmove on a mounted (or otherwise in use) LV might cause curruption of
> > your data.
> 
> In what cases could pvmove cause corruption on a mounted LV? Looking
> at the man page and scanning through pvmove.c, it seems to indicate
> that only a system crash during pvmove would corrupt the data. Is
> this the only case, or are there others?

Search back through the list for a response from Andrea Arcangeli.  We
need to track buffer_heads that have been trhough the make_request
function so we can really can flush the LV when suspending io for the
dureation of the move.  If you're not using raw io then the only
problem is a possible deadlock when under high memory pressure.

> If there are other possibilities for corruption, wouldn't it be a
> good idea to not allow pvmove's on PV's that contain mounted LVs?

IMO yes.

- Joe

[linux-lvm] pvmove question

[Peter V. Saveliev]

...

Hello. I have a VG on two software raid1 devices:

~ # pvs
  PV         VG      Fmt  Attr PSize  PFree 
  /dev/md0   hosting lvm2 a-   16.96G 16.96G
  /dev/md1   hosting lvm2 a-   16.96G  6.96G

I need to remove one raid (md1) from VG, but it is used:

~ # vgreduce hosting /dev/md1
  Physical volume "/dev/md1" still in use

But I cannot free it:

~ # pvmove /dev/md1 /dev/md0
  Unrecognised segment type mirror

Is there any solution? The system running lvm is a test box
and data stored on the VG is also unimportant; but I must
complete tests before running this system in production.

~ # uname -r
2.6.11-vs26-smp-rad4

~ # lvm version
File descriptor 5 left open
  LVM version:     2.01.10 (2005-05-03)
  Library version: 1.01.01 (2005-03-29)
  Driver version:  4.4.0


-- 
Peter V. Saveliev