[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