Re: DAR differential backup

zentara_at_highstream.net
Date: 05/19/04 

Date: Wed, 19 May 2004 09:35:46 -0400

On Mon, 17 May 2004 19:47:02 +0100, "ivan danicic" <ivan@goaway.spam>
wrote:

>
><zentara@highstream.net> wrote in message
>news:73vha0hg6obgmg09jibiq3o1llp75uvvjj@4ax.com...
>> On Sun, 16 May 2004 21:31:39 +0100, "ivan danicic" <ivan@goaway.spam>
>> wrote:
>>
>> >Hello All,
>> >Could you please give me a more or less precise definition of the command
>> >dar .... -A previous_ backup
>> >An explanation of type "the differential backup uses the archive
>> >previous_backup
>> >to decide what to back up" I don't find sufficient. For instance, is the
>> >date stamp of previous_backup
>> >relevant? Any comments gratefully received.
>> >Ivan.
>>
>> Ok here is an example:
>>
>> Say you want to make a first full backup of your system.
>> ( most of the variables are in darrootrc, or you can spell them out on
>> the commandline).
>>
>> ./dar -c /tmp/dar/root_full -v -N -B darhomerc
>>
>> That will create a set of archives named root_full with a numbering
>> system, if you specify to break the archives into chunks, like
>> root_full.1 root_full.2 etc.
>>
>>
>> The first differential backup will reference the root_full
>>
>> ./dar -c /tmp/root_diff0 -A /tmp/dar/root_full -v -N -B darrootrc
>>
>> will create root_diff0.1 root_full0.2 etc
>>
>>
>> The second differential backup will reference the root_diff0
>>
>> ./dar -c /tmp/root_diff1 -A /tmp/dar/root_diff0 -v -N -B darrootrc
>>
>> will create root_diff1.1 root_full1.2 etc
>>
>>
>> And so on. Dar keeps track of the secondary chunk numbers for you,
>>
>> If you keep track of the dates they are made, you can restore to any
>> date you want.
>>
>> Dar comes with alot of tutorials and docs, and all the features are
>> explained in there.
>>
>> Dar is very good and reliable, but you need to get used to it's syntax,
>> just like tar. :-)
>>
>> --
>> I'm not really a human, but I play one on earth.
>> http://zentara.net/japh.html
>Hello, I think that I misunderstood what goes on: from reading the
>'tutorial' I thought DAR looks only at the most recent archive; it
>says:"just before effectively starting to backup, dar will ask for ...the
>archive of reference." This archive seems to be the last one and is
>designated by the -A option. From what you say above this is not quite so,
>though I don't see where DAR gets information about previous archives.
>Please explain.
>Ivan
>

OK, dar gives you the option of which backup to reference from, which
may or not be useful to you, but it is flexible in case you wanted to do
it.

Dar keeps an internal catalog which it refers to in each archive. Look
at the "catalog" option in the docs. I don't bother to make a catalog,
I just let dar extract the catalog from the -A archive of reference".
The catalog can be kept as a separate file if you want, and you can tell
dar to use that catalog in the -A option. Read the docs and the
tutorial.

In the example above, say I'm going to make the third differential,
but for some reason I made so many changes, I wanted to forget about the
second differential backup, which I just made with the following.
 
>> ./dar -c /tmp/root_diff1 -A /tmp/dar/root_diff0 -v -N -B darrootrc
>>
>> will create root_diff1.1 root_full1.2 etc

I could remake the second differential by reissuing the above command,
and it will reference the first differential backup.

Or as it states in the docs, after you make a bunch a differential
backups, say 7, you may want to combine them all into one. So you could
delete all of your previous differentials, and remake a brand new first
differential taking the "root_full" as the reference archive.

The reference archive is just the "last reference point" from which
you want to extract the "differences to" into the differential archive.

The docs furthur state that if you have made alot of changes to your
system, and have alot of big differential backups, you may want to start
from scratch and just make another root_full to be your basis point. 

-- 
I'm not really a human, but I play one on earth.
http://zentara.net/japh.html

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