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Re: [libvirt] LVM storage pool with existing mirrored volumes



On Sun, Jan 17, 2010 at 03:44:28PM +0000, Ben Roberts wrote:
> Hi,
> 
> I tried to setup a lvm-backed storage pool, reusing an existing volume
> group which already contains a handful of mirrored logical volumes.
> 
> For reference, I am using lvm 2.02.56-r3, qemu-kvm 0.12.1.2 and libvirt
> 0.7.5 on an up-to-date ~amd64 gentoo system.
> 
> The first issue I encountered is when trying to activate the storage
> pool, the process fails with "internal error lvs command failed". This
> appears to be because the output of lvs is slightly different when using
> mirrored lvs, and is breaking the parser:
> 
> /sbin/lvs --separator , --noheadings --units b --unbuffered --nosuffix
> --options lv_name,origin,uuid,devices,seg_size,vg_extent_size bigpool
> 
> vms,,0PzrRS-8Ljs-SUq0-ywFH-BI3d-RI0V-aibupu,vms_mimage_0(0),vms_mimage_1(0),107374182400,4194304
> 
> backups,,Snk2NL-oJe3-GpTL-Qihs-ZjjG-xPyj-ufmwCp,backups_mimage_0(0),backups_mimage_1(0),214748364800,4194304
> 
> The device column of output would normally contain something like
> "/dev/sda(1234)", but here contains "vms_mimage_0(0),vms_mimage_1(0).
> 
> This is causing the parser to misinterpret the output, and it believes
> the lv name to be suffixed with a trailing comma, eg "vms,". When trying
> to access "/dev/bigpool/vms,", the command errors with File or Directory
> not Found.
> 
> When adding the --all parameter to lvs, the hidden mirroring lvs are
> visible, and these have the expected structure:
> 
> vms,,0PzrRS-8Ljs-SUq0-ywFH-BI3d-RI0V-aibupu,vms_mimage_0(0),vms_mimage_1(0),107374182400,4194304
> [vms_mlog],,vnOzg8-ynKc-kM8F-RKdM-xXC0-PJlG-qcgmFh,/dev/sda2(0),4194304,4194304
> [vms_mimage_0],,2pXjHt-aARa-FOO7-ZL6N-ahpu-ebdr-P6Qxj3,/dev/sdb1(0),107374182400,4194304
> [vms_mimage_1],,ITd8CT-JpKi-Y2a6-a4jc-2yDa-9VmG-gWgRd8,/dev/sdc1(51200),107374182400,4194304
> 
> Presumably, without the --all parameter and listing the internal
> mirroring volumes, libvirt will miscalculate sizes of LVs in the VG.

Yes, the output of mirrored devices is definitely going to cause 
problems for our parsing. This doesn't look all that easy to fix to
me, but we'll clearly have to figure out some way to cope with this.


Daniel
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