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Re: [Xen-users] Is XVD live resize possible?

I think the developers have kind of let this one go.

Once upon a time, in addition to block-detach and block-attach there was also block-configure.  Block-configure supposedly told the inner DomU to refresh its idea of the block device.  It stopped working a while back, a few people complained, it was never fixed.

I haven't tested it, but this would be the "right way" to do it...if it worked.

On Apr 6, 2008, at 6:23 AM, Andy Smith wrote:

On Sun, Apr 06, 2008 at 12:09:37PM +0100, Nico Kadel-Garcia wrote:
Ferenc Wagner wrote:
No I can lvresize xenimages/stan in dom0, but the domU stays ignorant
of this change.  How could I propagate the resize to the domU without
rebooting or temporarily breaking its connection to /dev/xvda?  Sort
of a SCSI rescan, perhaps?

You have to resize the *file system* on the partition. Whether you can
use a 'rescue CD' inside the virtualized environment, to resize your
partitions, is an interesting question and may depend on your installed
OS quite a bit. You can certainly resize non-'/' partitions from the
live OS, and use such an environment to re-run grub if your boot loader
has moved or gotten confused.

Have you ever actually tried this with a block device exported to a
domU?  Because as far as I know, you cannot make Xen see the change
in size of the block device without detaching it and then attaching it
again (from dom0).

This question comes up repeatedly on this list and someone usually
says "you need to resize the filesystem as well" without
understanding that the domU is not seeing the change of size in the
block device.  Without which it is of course impossible to resize
whatever filesystem is on it.


A technique I have used for customers that required to add and
remove disk space without any loss of service is to give them their
/ on one block device and then supply them with multiple other block
devices which they use as LVM PVs.  These can be added and removed with
LVM inside the domU, with the data shifting off/on the different
devices as needed.

Obvious downsides to this approach are the added complexity, small
performance loss from LVM-on-xvd*-on-LVM, and lack of easy
access to the data from dom0.

Or there is always NFS..  I don't know how or even if iSCSI, AoE or
NBD cope with changing sizes of block devices but that is perhaps
something to explore.

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Jayson Vantuyl
Systems Architect
1 866 518 9275 ext 204

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