[linux-lvm] Snapshot COW area on different PV / device

[linux-lvm] Snapshot COW area on different PV / device

[Hannes Dorbath]

Hello,

I suffer from massive I/O trashing, due to the snapshot COW area being 
located on the same physical device as the origin. The machine now has a 
second disk array, that I'd like to dedicate to snapshot COW data. My 
problem now is that I fail to see from the documentation how to create a 
snapshot, which has its COW area located on another device. The setup 
currently looks like:

VG     #PV #LV #SN Attr   VSize   VFree
data     1   1   0 wz--c- 437.62G      0
cow1     1   0   0 wz--c- 232.82G 232.82G
cow2     1   0   0 wz--c- 232.82G 232.82G

LV     VG     Attr   LSize   Origin Snap%  Move Log Copy%
data   data   -wc-ao 437.62G

data is the LV where production data is located, and the cow1 and cow2 
VGs should be used for snapshots. Can someone give me an example on the 
lvcreate syntax to archive this? I tried various things, but end up with 
error messages like "Could not fine LV <foo> in PV <bar>".

Thanks in advance.


-- 
Regards,
Hannes Dorbath

Re: [linux-lvm] Snapshot COW area on different PV / device

[Jonathan Brassow]

you will need more than on device in your volume group.  Example:
$> pvcreate /dev/sd[ab]
$> vgcreate vg /dev/sd[ab]
$> lvcreate -n lv -L 200G vg /dev/sda
$> lvcreate -s -n snap -L 20G vg/lv /dev/sdb

The cow will be located on sdb, while the origin will be located on sda.

  brassow

On Aug 27, 2007, at 3:53 AM, Hannes Dorbath wrote:

> Hello,
>
> I suffer from massive I/O trashing, due to the snapshot COW area  
> being located on the same physical device as the origin. The  
> machine now has a second disk array, that I'd like to dedicate to  
> snapshot COW data. My problem now is that I fail to see from the  
> documentation how to create a snapshot, which has its COW area  
> located on another device. The setup currently looks like:
>
> VG     #PV #LV #SN Attr   VSize   VFree
> data     1   1   0 wz--c- 437.62G      0
> cow1     1   0   0 wz--c- 232.82G 232.82G
> cow2     1   0   0 wz--c- 232.82G 232.82G
>
> LV     VG     Attr   LSize   Origin Snap%  Move Log Copy%
> data   data   -wc-ao 437.62G
>
> data is the LV where production data is located, and the cow1 and  
> cow2 VGs should be used for snapshots. Can someone give me an  
> example on the lvcreate syntax to archive this? I tried various  
> things, but end up with error messages like "Could not fine LV  
> <foo> in PV <bar>".
>
> Thanks in advance.
>
>
> -- 
> Regards,
> Hannes Dorbath
>
> _______________________________________________
> linux-lvm mailing list
> linux-lvm@redhat.com
> https://www.redhat.com/mailman/listinfo/linux-lvm
> read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/