Re: enlarging snapshot volume automatically?

 --- Joe Thornber <thornber@xxxxxxxxxxx> wrote: > On
Tue, Apr 29, 2003 at 08:01:57PM +0900, Kwon
> SoonSon wrote:
> > > 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.
> 
> There are a couple of arguments that you can give to
> your script that
> will allow the sys admin to control it as he likes:
> 
> i) Poll period, eg, if 5 minutes is too infrequent,
> set it to 1 minute, 30 seconds etc.
> 
> ii) The threshold at which the script decides to
> extend the volume. eg 80% full.
> 
> > 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?
> 
> The kernel knows nothing about extents or volume
> groups, so no.
> 
> > 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?
> 
> We've been trying hard to get rid of complex
> behaviour like this from
> the kernel, it belongs in userland, this is _policy_
> not mechanism.
> 
> Why not just allocate more space to the snapshot to
> start with ?

Thanks very much for your quick reply.
I just wanted to fully automate the snapshot
management
without any user intervention as long as there are
unused
spaces somewhere in the volume group or physical
volume. :-)

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