deja-dup issue

[Colin Law]

On 16 May 2016 at 14:37, Tony Arnold <tony.arnold at manchester.ac.uk> wrote:
> Colin,
>
> On 16/05/16 13:42, Colin Law wrote:
>> On 16 May 2016 at 13:27, Jatin khatri <khatri.jatin at gmail.com> wrote:
>>> On Sunday 15 May 2016 12:55 PM, Petter Adsen wrote:
>>>
>>> On Sun, 15 May 2016 08:09:30 +0100
>>> Colin Law <clanlaw at gmail.com> wrote:
>>>
>>> On 15 May 2016 at 05:07, Jatin khatri <khatri.jatin at gmail.com> wrote:
>
>>> One more question, Does it support Compression and Incremental backup ( same
>>> like Deja-Dup)  ?
>>
>> Assuming that you mean backintime then no to compression.  If a file
>> has not changed then hard links are used in the backup so that the
>> unchanged file takes up (effectively) no space.
>
> Just to add to this. If the backups on a different file system to the
> source, then copies are made. Or is that only for the first snapshot? Do
> subsequent snapshots use hard links to the backed up version for
> unchanged files?

The links are entirely within the backup. The first time a file is
encountered it is copied to the backup, then later snapshots link to
the copy.  So if you did a backup and then immediately backed up again
then the second backup would be entirely made of links to the first.
Then the backup device could be removed (if it were on a removable
disc for example) and read on a different machine and all the files
would be there in both snapshots.  That assumes the backup is onto a
file system that supports hard links of course, otherwise backintime
has to make new copies each time.  The backup can be to a different
machine using, for example, ssh.

Colin