On Thu, 29 Mar 2001, Peter Rundle wrote:
> Sluggers,
>
> Does anyone know if there is a Veritas equivilent to doing file
> based snapshots in Linux. I've been told that this is available
> in the Logical Volume Manager (LVM) but looking at their site it
> appears that they do volume based snapshots not file based.
> And these snapshots in fact copy the entire data.
>
> The basic method is like this,
[snip]
just for future reference, this technique is often refered to as "copy on
write".
i.e - This is used whenever a translation map translates virtual addresses to
physical addresses. When a copy is made, have the entries of the duplicate point
at the original data (just like the original entries), and both sets are marked
as "read only". Reads still go to the original data. When a write is performed,
it's trapped and a real copy is then made before continuing with the write
operation.
Linux and most Unix's do this when a program fork()'s. Hell, I think
the Gimp even does this now when an image is duplicated.
As for your original question, I don't know. Have you asked on the LVM list?
I wouldn't be surprised if someone is working on something like this.
bye
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Ian Tester *8)# \7\ LINUX: because geeks will find a way
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