[linux-lvm] Mapping LVs to physical device

[linux-lvm] Mapping LVs to physical device

[Chris Farey]

I have a requirement to be able to work out which areas of a physical 
device assigned to LVM are being used by various logical volumes. I 
haven't found any easy way to do this using an API, so I've resorted to 
spawning off lvm commands and interpretting the output.

I can use lvdisplay to map logical extents to physical extents, but I 
still need to know where the extents start on the physical device, and I 
can't find a good way of doing that.

pvck tells me the offset and the size of the metadata, and assuming that 
the first extent starts after the metadata seems to work. But pvck 
doesn't seem to be present in older versions of LVM (or one of my 
systems starts running them gets killed), and the help implies its doing 
some checks too (and lengthly checks would be bad in my application).

Is there a better way to map the Logical Block Addresses of LVs to 
physical disks?

Chris Farey

Re: [linux-lvm] Mapping LVs to physical device

[Milan Broz]

Chris Farey wrote:
> I have a requirement to be able to work out which areas of a physical 
> device assigned to LVM are being used by various logical volumes. I 
> haven't found any easy way to do this using an API, so I've resorted to 
> spawning off lvm commands and interpretting the output.

you can report all attributes using pvs/lvs/vgs, like this
 
pvs -o +devices

lvs --segments -o +seg_pe_ranges

... for list of available attributes just run "pvs -o help"

Milan
--
mbroz@redhat.com

Re: [linux-lvm] Mapping LVs to physical device

[Stuart D. Gathman]

On Tue, 30 Jun 2009, Chris Farey wrote:

> I have a requirement to be able to work out which areas of a physical device
> assigned to LVM are being used by various logical volumes. I haven't found any
> easy way to do this using an API, so I've resorted to spawning off lvm
> commands and interpretting the output.

It is also useful to go the other way: given a physical sector, figure out
which LV it is in and the offset.  When there is a physical disk error
(and no mirroring or such), it is useful to map it to an offset in a LV,
and then to a file.  Modern disks can "heal" themselves by writing over 
the sector (copying, repairing or replacing, and then overwriting the file).

-- 
	      Stuart D. Gathman <stuart@bmsi.com>
    Business Management Systems Inc.  Phone: 703 591-0911 Fax: 703 591-6154
"Confutatis maledictis, flammis acribus addictis" - background song for
a Microsoft sponsored "Where do you want to go from here?" commercial.