Re: [Xen-devel] About Copy-on-Write in Xen

[Bin Ren <br260@xxxxxxxxx>]

On 16 Jan 2004, at 16:36, Ian Pratt wrote:
> > In Xen, VBDs are implemented as 'extents'. One 'extent' is a group of
> > contiguous sectors of the real disks. VBDs can grow by adding extra
> > extents from the underlying real disks. Obviously, VBDs work at a
> > much lower level.
> >
> > Therefore, you can say, you have created a VBD of 4G but actually
> > starts with only 500M. Whenever the free space drops below a
> > threshold, extra extents are automatically added. This function is
> > already present in 1.2 and 1.3
> Erm, no.
>
> virtual disks may be extended or contracted, but this is not
> currently automatic: the vd tools must be used to extend the
> virtual disk, and then typically the guest will need to resize
> the file system on the virtual disk (I believe ext3 supports
> on-line resizing, but not automatically).
Ian, thanks for pointing this out. I messed the words up when I tried to
say: the function extent adding/removing has been present; but for
automatic resizing, a script should be created.

In addition to ext3, reiserfs has good support for online resizing,
i.e. without unmount.

-- Bin



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