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



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


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