On Tue, Oct 21, 2014 at 03:34:44PM +0100, Laurie Brown wrote:
On 21/10/14 13:38, Chris Green wrote:
[SNIP]
It was on my original shortlist a while back but I chose rsnapshot instead because rsnapshot does snapshots (i.e. each backup looks like a complete snapshot of everything you're backing up) whereas rdiff-backup does 'masters' plus diffs over a period.
This is a *big* distinction IMHO. With rdiff-backup you have to reconstruct any file you want to restore unless it happens to be unchanged since the last 'master' backup. Also as I understand how rdiff-backup works the diffs get more and more 'distant' as you make more and more backups.
With rsnapshot (or my more recent home-made system) hard links are used to save space where files haven't changed so every backup you make is a complete set of files, you can just copy the file back from the backup you select, no reconstruction needed.
I much prefer snapshots as they seem to me much safer and more robust.
So... Why ask about incrementals in the subject of the OP if you've already decided to use snapshots only?
Because, to my mind and many others, incremental can mean differential or snapshot! :-)
The advantage of incrementals is the space saved. And, of course, you can always take an annual/quarterly/monthly/whatever snapshot of the incrementals, archive it to release space and then start again... In fact, that's a basic requirement for sensible file management.
I think you'll find that there's very little difference. In reality a lot more than 90% of what you save over the long term doesn't change so it's only the efficiency or otherwise of saving the changed bits that affects how your backups grow.
My snapshots save almost 200Gb of files, each snapshot after the first one occupies between 300Mb and 400Mb, so I can save a lot of snapshots without using much space. Even a hundred snapshots would take only 40Gb or so more.
Obviously if lots of files change then the snapshots start eating more space but that applies to differential backups too.