Re: [Xen-users] resize xen disk file

[Rudi Ahlers <Rudi@xxxxxxxxxxx>]

Javier Guerra wrote:
> On Thu, Mar 6, 2008 at 4:16 PM, Rudi Ahlers <Rudi@xxxxxxxxxxx> wrote:
>   
> > Martin Fernandez wrote:
> >  > I resized the file disk using:
> >  > dd if=/dev/zero of=*image* bs=1M conv=notrunc count=1 seek=10240
> >  Can someone please explain to me what this command does? I also want to
> >     
> 'dd' copies 'count' blocks of size 'bs' from 'if' to 'of', first
> advancing (from start) 'seek' blocks.
>
> in this case, it advances to 10G (10240*1M), and writes 1M of zeroes.
> if the image file was smaller than that, it would grow.
>   
Thanx :)

What does the "conv=notrunc" mean? And does / will it simply append the 
extra blocks to the existing ones? Or how does it know where to put it?
> >  And is it safe to resize an VM image while it's running?
> >     
> sure.  to the VM it's simply that the block device won't complain for
> access to blocks that it wasn't accessing anyway.
>
> example:
> - you have a 5G image file, put an ext3 filesystem on it.  mkfs checks
> the device size once and does the ondisk structures so that you won't
> try to access beyond the end of the device when using the filesystem.
>
> - start VM:
>     - checks device size, shows it in /proc/partitions
>     - mounts fs, uses it to access, never writes beyond 5G
>
> - in Dom0 you grow it to 10G.  now if you wrote to the device at the
> 7G point, it could work, but the kernel still beleives it's just 5G,
> so it would fail before trying.
>
> - in VM do a partscan.  /proc/partitions is updated, now it shows 10G
> and if you wrote to the 7G point it would work; but the filesystem
> still is 5G
>
> - in VM do a resizefs, this is the part that really affects upper
> layers, but there's lots of experience in doing it well, and these
> days most filesystems can do it online. (at least ReiserFS, ext3, XFS)
>
> the only 'scary' thing is updating all layers in the *correct* order.
> in this example, the image file directly contains the ext3 fs; but if
> you have LVM, there are at least a couple more (PV and LV)
>   
This helps quite a lot. Do I understand correctly that there's no point 
in setting up a LVM on the VM then?
So, to safely resize the current VM's space, I do the following:

xm save vm01
xm destroy vm01

Then I increase the image

dd if=/dev/zero of=/home/vm/vm01.im bs=1M conv=notrunc count=1 seek=30720

after that I need to run partscan? I don't see such a command on the VM, what 
is it part of?

After I install partscan, then how do I use it?

Then, I need to run resize2fs, what is the correct syntax?

This is the current VM's output
root@vps01 [~]# df -H
Filesystem             Size   Used  Avail Use% Mounted on
/dev/mapper/VolGroup00-LogVol00
                      9.8G   6.6G   2.7G  71% /
/dev/xvda1             104M    20M    79M  21% /boot
tmpfs                  537M      0   537M   0% /dev/shm
/usr/tmpDSK            508M    42M   441M   9% /tmp




--

Kind Regards
Rudi Ahlers
CEO, SoftDux

Web:   http://www.SoftDux.com
Check out my technical blog, http://blog.softdux.com for Linux or other 
technical stuff, or visit http://www.WebHostingTalk.co.za for Web Hosting stugg


_______________________________________________
Xen-users mailing list
Xen-users@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-users