[linux-lvm] 'snapshot' target still experimental :-(

[Ming Zhang]

On Wed, 2006-02-01 at 16:51 -0500, Brian J. Murrell wrote:
> On Wed, 2006-02-01 at 13:29 -0800, Dan Stromberg wrote:
> > It just maintains a series of hardlink trees, so any time a file is
> > deleted or added, the actual disk usage increase is only due to the
> > changes.
> 
> Yes, this is quite a popular technique.  To be clear though, a change in
> a file does not consume just the amount of the change in the file on the
> backup target, but it consumes the entire size of the new file.  A
> not-so-insignificant amount for very large files.  This is where a
> (block level or filesystem level) snapshotting scheme would excel as it
> would likely only consume an amount of space rounded up to the next
> "unit" size more even for changes within a file.

it depends.

assume u have a huge text file. u change 1 char, the snapshot is useful.
u add one line at the beginning, the snapshot is useless here.

the offset shift.

some delta tech will be useful here.


> 
> Indeed (and to keep quite on topic), perhaps rather than hardlink trees,
> LVM snapshots would be even more space efficient.  Maybe that is what
> this thread has been about.  I just jumped in.  Apologies if it was.
> 
> b.
> 
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