[linux-lvm] "cannot allocate memory" when trying to do a snapshot?

[linux-lvm] "cannot allocate memory" when trying to do a snapshot?

[Tomasz Chmielewski]

I have a server with ~1.5T PV, on which I have several logial volumes (LVs).

I decided to do a snapshot for five of these LVs, and it succeeded, but 
only few times.

   dom-dc1           san1 owi-ao   8.00G
   dom-oss1          san1 owi-ao  16.00G
   dom-sql1          san1 owi-ao   8.00G
   dom-sql1-2        san1 owi-ao  50.00G
   dom-ts1           san1 owi-ao  16.00G

For each of the LVs, I made 5G snapshots.
I could make three snapshots for all of them, but the fourth snapshot 
failed for some LVs (in all, I could only make 18 * 5GB snapshots).

Why?

I'm using Debian Etch, with its 2.6.18 64 bit kernel.
The machine has 512 MB RAM, and 3 GB swap:

# free
              total       used       free     shared    buffers     cached
Mem:        512204     492212      19992          0     297784      17864
-/+ buffers/cache:     176564     335640
Swap:      3145720          0    3145720



I've searched the list, and a similar cases appeared on the list in 
2002/2003, most without any reply - but it was LVM1 / 2.4.x times.


-- 
Tomasz Chmielewski

Re: [linux-lvm] "cannot allocate memory" when trying to do a snapshot?

[Tomasz Chmielewski]

Tomasz Chmielewski schrieb:
> I have a server with ~1.5T PV, on which I have several logial volumes 
> (LVs).
> 
> I decided to do a snapshot for five of these LVs, and it succeeded, but 
> only few times.
> 
>   dom-dc1           san1 owi-ao   8.00G
>   dom-oss1          san1 owi-ao  16.00G
>   dom-sql1          san1 owi-ao   8.00G
>   dom-sql1-2        san1 owi-ao  50.00G
>   dom-ts1           san1 owi-ao  16.00G
> 
> For each of the LVs, I made 5G snapshots.
> I could make three snapshots for all of them, but the fourth snapshot 
> failed for some LVs (in all, I could only make 18 * 5GB snapshots).
> 
> Why?
> 
> I'm using Debian Etch, with its 2.6.18 64 bit kernel.
> The machine has 512 MB RAM, and 3 GB swap:

Some more info on that.
Apparently, this whole snapshotting thing is not very stable, and there 
are bugs in it.

I just played a bit more with creating snapshots.

Below, although creating a snapshot fails, a new logical volume is created:

# lvcreate -L100G -s -n backup-snapshot /dev/san1/backup
File descriptor 3 left open
File descriptor 5 left open
File descriptor 7 left open
   device-mapper: reload ioctl failed: Cannot allocate memory
   Failed to suspend origin backup


# lvs
File descriptor 3 left open
File descriptor 5 left open
File descriptor 7 left open
   LV                     VG   Attr   LSize   Origin          Snap% 
Move Log Copy%
   backup                 san1 -wi-ao 628.28G
   backup-snapshot        san1 -wi-d- 100.00G
(...)


So, if it fails, at least it shouldn't create any phantom volumes.

Does lvm snapshotting work any better with newer kernels?


-- 
Tomasz Chmielewski
http://wpkg.org

Re: [linux-lvm] "cannot allocate memory" when trying to do a snapshot?

[Brian J. Murrell]

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On Mon, 2007-08-27 at 18:08 +0200, Tomasz Chmielewski wrote:
> 
> Some more info on that.
> Apparently, this whole snapshotting thing is not very stable, and there 
> are bugs in it.

This whole snapshotting thing is a known and fixed bug.  I opened a bug
about it in RH's bugzilla about a year ago but am unable to log back in
there to find it specifically for you.  Search for bugs reported by
anyone @interlinx.bc.ca.  Try the word "kcopy" in the bug if there are
too many listed.

Cheers,
b.

-- 
My other computer is your Microsoft Windows server.

Brian J. Murrell

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Re: [linux-lvm] "cannot allocate memory" when trying to do a snapshot?

[Tomasz Chmielewski]

Brian J. Murrell schrieb:
> On Mon, 2007-08-27 at 18:08 +0200, Tomasz Chmielewski wrote:
>> Some more info on that.
>> Apparently, this whole snapshotting thing is not very stable, and there 
>> are bugs in it.
> 
> This whole snapshotting thing is a known and fixed bug.  I opened a bug
> about it in RH's bugzilla about a year ago but am unable to log back in
> there to find it specifically for you.  Search for bugs reported by
> anyone @interlinx.bc.ca.  Try the word "kcopy" in the bug if there are
> too many listed.

Looks like it's here:

https://bugzilla.redhat.com/show_bug.cgi?id=208172

Let's see if upgrading the kernel helps...


-- 
Tomasz Chmielewski
http://wpkg.org

Re: [linux-lvm] "cannot allocate memory" when trying to do a snapshot?

[Brian J. Murrell]

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On Mon, 2007-08-27 at 18:25 +0200, Tomasz Chmielewski wrote:
> 
> Looks like it's here:
> 
> https://bugzilla.redhat.com/show_bug.cgi?id=208172

Yup.  That's the one my bug 191531 was dup'd to.

> Let's see if upgrading the kernel helps...

Let us know.

b.

-- 
My other computer is your Microsoft Windows server.

Brian J. Murrell

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Re: [linux-lvm] "cannot allocate memory" when trying to do a snapshot?

[Tomasz Chmielewski]

Brian J. Murrell schrieb:
> On Mon, 2007-08-27 at 18:25 +0200, Tomasz Chmielewski wrote:
>> Looks like it's here:
>>
>> https://bugzilla.redhat.com/show_bug.cgi?id=208172
> 
> Yup.  That's the one my bug 191531 was dup'd to.
> 
>> Let's see if upgrading the kernel helps...
> 
> Let us know.

It looks that it helped.

However, now it's possible to create a snapshot that is no longer 
possible to remove...

See my other thread ("how much memory does LVM need? oom-killer comes").


-- 
Tomasz Chmielewski
http://wpkg.org