Re: enlarging snapshot volume automatically?

 --- Joe Thornber <thornber@xxxxxxxxxxx> wrote: > On
Tue, Apr 29, 2003 at 05:31:43PM +0900, Kwon
> SoonSon wrote:
> > Hi, I am thinking of a possible way to enlarge the
> > snapshot automatically when there is no space for
> > copy-on-write operation.
> > 
> > I thought when the kernel fails to allocate more
> > space, following the same way when the user 
> > enlarges that snapshot volume manually.
> > 
> > But I am not sure if this is possible because the
> > low device-mapper level only cares for the target
> > type and mapping information. (as far as I know.)
> > 
> > If there is a good idea on how to automatically
> > allocate more space whenever needed, please
> > let me know. (Or if there is any restriction on
> doing
> > this, let me know also. :-))
> > 
> > If LVM can allocate more space to snapshot
> > without the user's manual operation, that would be
> > a very nice improvement.
> 
> Write a sh script that checks how much free space
> there is every 5
> minutes and extends if neccessary ?

Thanks very much for your quick reply.
That sounds a very interesting idea but I think if
many
blocks are overwritten exceeding the remaining free
space of a specific snapshot within 5 minutes,
then the snapshot would be gone.

Isn't there any other solution that always guarantees
a safer copy-on-write as long as there are unused
blocks
in the volume group? Is it impossible to run a
user-level
command(lvextend?) in kernel so that it can get more
space for that snapshot volume as soon as it detects
the space shortage?

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