[linux-lvm] Limitation: only < 32 snapshots possible

[linux-lvm] Limitation: only < 32 snapshots possible

[Daniel Schwager]

Hi together,

i create 5 LV's (e.g. play1..n) and therefore, i created 10 snapshots
for each LV. After 32 snapshots (should 5*10 = 50 snapshots), i got the
following error:
    "device-mapper: reload ioctl failed: Cannot allocate memory"

My versions (on debian etch):
    xentor:/etc/lvm# lvm version
      LVM version:     2.02.07 (2006-07-17)
      Library version: 1.02.08 (2006-07-17)
      Driver version:  4.7.0

I looked arround and found  
http://sources.redhat.com/lvm2/wiki/FrequentlyAskedQuestions      (last 
topic on page):

    *  > Known problem - will be partially solved by new DM-IO interface.
    *  > But anyway, current snapshot implementation is not properly
      designed for such type of operation (many snapshots will
      significantly slow down all IO).

QUESTION: Is this limitiation fixed in the current version 2.02.24 from 
ftp://sources.redhat.com/pub/lvm2

Thanks for helping

regards

Danny

BTW: I want to clone (means create LVMs-snapshot) about 40 xen vm's 
running on 4 xen-server ..
therefore it would nice to use the LVM2-snapshot-feature (instead of 
GFS/OCFS2).

Re: [linux-lvm] Limitation: only < 32 snapshots possible

[Daniel Schwager]

>> QUESTION: Is this limitiation fixed in the current version 2.02.24 from 
>> ftp://sources.redhat.com/pub/lvm2
>>     
> These are limitations of the existing kernel implementation, not userspace.
>   
Hi Alasdair,

is there a kernel patch to fix this limiation ?

regards

Danny

Re: [linux-lvm] Limitation: only < 32 snapshots possible

[Alasdair G Kergon]

On Sat, Apr 14, 2007 at 03:27:03PM +0200, Daniel Schwager wrote:
> QUESTION: Is this limitiation fixed in the current version 2.02.24 from 
> ftp://sources.redhat.com/pub/lvm2
 
These are limitations of the existing kernel implementation, not userspace.

Alasdair
-- 
agk@redhat.com