lazy mirror / live backup

[Bernd Walter]

On Sat, Apr 21, 2007 at 01:38:31AM +0100, Mike Wolman wrote:
> My only concern is zfs is quite heavy weight (memory wise) compared to 
> gmirror and ufs for a simple laptop/desktop setup which you may just want 
> to replicate the entire drive and grab the ggatec device and be ready to 
> run should anything happen to the machine.

Yes - that's unfortunately true.

> Im sure there are other situations where running zfs on the available 
> hardware is not an option compared to gmirror - im not sure what the 
> recommended amount for freebsd but as far as i can rember the suggested 
> about for solaris is 1Gb - comparing to gmirror i think i have run it on a 
> machine doing simple home fileserving with 128Mb.

Ever thought about UFS snapshots backed with rsync?
You get a consitent pseudo image of your running filesystem with
unallocated blocks represented as zeros.
rsync now allows comparing file chunks and copies only differences.
Still every block need to be read, though.

vbackup from devel/plan9port stores checksums and allows offering
only different blocks to the other side.
venti - the backing store behind vbackup - allows compression and
single storage of different blocks with same data, which reduces
the required backup capacity very impressive.
My expirience with vbackup is that this mechanism is fast enough
as long as there are no hughe differences.

-- 
B.Walter                http://www.bwct.de      http://www.fizon.de
bernd at bwct.de           info at bwct.de            support at fizon.de