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

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Subject: Re: [Xen-users] Is XVD live resize possible?
From: Andy Smith <andy@xxxxxxxxxxxxxx>
Date: Sun, 6 Apr 2008 13:23:15 +0000
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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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