Snapshots and Sessions?

[ManChicken]

I have a backup set consisting of a series of LTO-3 tapes. For this set I typically have just used 'Archive Files' for dumping a project's data to LTO for long-term storage/backup as they are all very large media files that must be moved off the systems they came from when a project is complete.

 

If I use "Session Contents" and select my backup set, I can see all of the sessions (11 so far), select any one and hit Browse, and see all of the files archived for that particular session.

 

When it comes time to restore a project that I need to revise, I use Restore, select my backup set, then only see a handful of snapshots to choose from. If I hit 'More Snapshots', I see the full list of 11, but then have to Retrieve the one I want.

 

So why is it that one knows (Session Contents), yet the other doesn't (Restore) and makes me shuttle the entire last tape in the set to fetch the snapshot, and then shuttle it back so I can put in the actual tape it needs to restore from?

[SmudgerDan]

Hi ManChicken,

 

I am new to the Retrospec world after the last guy left and it is now my job to look after the company's data so this comment may not be the right.

 

From what I can see sessions are "writes" to the backup set, so any time any files (even if just one completed of an entire volumn) are written.

 

Snap shots how ever are when you have the entire volumn at a particular time. This snap shot could be made of of many sessions.

 

So for example the entire volumn is backed up onto the backup set on the 1st of the month. The next scheduled backup for this happens on the 2nd of the month, but fails after just 5%.

 

Now we have 2 sessions recorded (a 100% and then just a 5%) but there will only be one snap shot dated the 1st of the month.

 

Now coming to your restore question. Remember retrospect (if setup like this) only copies changed files. So your project file may have files which have never changed since the first backup (which maybe on the first tape) and also contain files which where changed regularly and resently (which maybe on the last tape).

 

This is just a guess, as I said I have been using Retrospect for about 2mins

[ManChicken]

Well I think I get the distinction between sessions and snapshots, but my underlying question is why can I look at all of the files in any snapshot but when I go to restore those files I have to re-fetch the session contents off tape first (in the event the one I want is not already listed?)

 

[rhwalker]

Well I think I get the distinction between sessions and snapshots

Perhaps, but just to make sure, here is my explanation in another thread:

The Retrospect paradigm - the Snapshot Illusion

 

but my underlying question is why can I look at all of the files in any snapshot but when I go to restore those files I have to re-fetch the session contents off tape first (in the event the one I want is not already listed?)

To specifically answer your question, it's simply a design decision ("feature") of the program that only the most recent snapshot is shown by default. You can ask the program to recreate older snapshots and, to do so, it has to analyze the backup set from the beginning (remember, under the hood it's still a "full backup plus incrementals" system) and figure out what files were there at the time of the requested snapshot.

 

Once a snapshot has been added to the catalog view, it will stay there (unless groomed out).

 

It's just a design decision to keep the amount of data in the catalog to a manageable size. Remember, the catalog is simply a database index into the various sessions in the backup set, telling where all of the files, which were present at the time of the snapshot, are located in the various sessions in the backup set.

 

Think database.

 

Clearer?

 

Russ