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

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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