[dm-devel] Problem when creating snashots

[Milan Broz]

The problem with limited number of snapshots is caused by the using
big common mempool in dm-io module.
(This can happen even you have a lot of free memory...)

There are new dm-io patches which introduce new dm-io interface
(using private mempools) and solving this type of snapshot limitation.

Patches are currently in review and will probably change a bit,
but I hope it will in 2.6.19 kernel.

Milan

--
mbroz at redhat.com

The MoonSeeker napsal(a):
> Yes I really need it. I have to create a virtual network editor for my
> diploma project. So I have found many virtual solutions but the bestest
> for our project is OpenVZ. Unfortunatly, OpenVZ don't offer the copy on
> write with his solution, after many tests, I have found a solution based
> on LVM.
> 
> The main idea is to have a Virtual Private Server Core and lot of
> Virtual Private Server who are a snapshot of the Virtual Server Core.
> Now the problem is the limitation of VLM, I need more than 32 servers
> (32 snapshots). Will this limitation incresed in futur futur released of
> LVM? Or can we broke this limitation?
> 
> Have you a solution, it's relly urgent for me...
> 
> Thanks you
> 
> 
> Le 26 sept. 06 à 23:14, Jan Blunck a écrit :
> 
>> On Tue, Sep 26, The MoonSeeker wrote:
>>
>>> I'd like to create many snaphot of an image but I've got when I
>>> attemp to create the 32th snapshot :
>>>
>>> root at B03:/diplome# lvcreate -s -L150M -n 232 /dev/openvz/vps-core
>>>   Rounding up size to full physical extent 152.00 MB
>>>   device-mapper: reload ioctl failed: Ne peut allouer de la mémoire
>>>   Failed to suspend origin vps-core
>>>
>>> I don't understand the error..
>>
>> I'm not a native french speaker (hint!) but I assume you run out of
>> memory.
>>
>> Yes there are limitations to the number of snapshots. For every single
>> snapshot we have to allocate memory for copying the chunks to the
>> exception
>> store.
>>
>> Do you really need that many snapshots at the same time?
>>
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> 
> 
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