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Hi,

 

I am a computer consultant and started working with a new client that uses Retrospect and I have some concerns.

 

The client has three tape libraries, each with 10 tape cartridges. They have about 1TB of data to backup.

 

The person doing the backups told me this:

He did a full backup 6 weeks ago, but does not really ever need to do one

He leaves on library in for a week and then rotates it with one of the other two. He does not do a full backup after switching libraries.

He feels he can do a complete restore of the server from any the cartridges, of course up to the time he took it out.

Is this correct?

 

That’s this is real important

 

Bob

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Well, you didn't give a full problem statement. Please understand that I'm not trying to be condescending here. Retrospect's terminology is different from that used by the rest of the industry.

 

Retrospect uses a "snapshot" paradigm to give a different view into a backup set than what is really happening under the hood. Basically, Retrospect's "Normal" backup is what other programs call "incremental" except that, the first time it is done, to an empty backup set, it does what other programs call a "Full Backup" (because the backup set is empty) and so everything becomes "incremental" (needed to be backed up). Other programs back up "incrementally" based on a time stamp or some such, backing up all files since that point. Retrospect backs up whatever it has to so that the backup set holds everything needed to restore the source to its state at the time of the backup. If a file is already in the backup set, it doesn't get backed up again (well, you can fine tune this so that some files always get backed up, etc., to handle some odd issues with database range locking, etc.). But under the hood, it adds what files it needs. The most recent snapshot is always available, but you can "add" earlier snapshots to restore to an earlier point in time, or to get multiple versions of files, in which case Retrospect just scans the backup set from the beginning and reconstructs what the "snapshot" was at the point you want one added, based on what files it had to back up at that point. So, a snapshot is the accumulated history from the start of the backup set, and Retrospect also notes deletions, renames, etc., so that you can browse snapshots just as if you were browsing the disk at the instant it was backed up.

 

Here's what I assumed from what your backup person told you:

 

Because the person doing the backups stated that he did a "Full Backup" six weeks ago (Retrospect doesn't have a "Full Backup" setting; it backs up what it needs to), I assumed that he was using language that you would understand. He probably did a "Recycle" backup at that point (which marks the backup set as empty and reuses the tape members) or else he erased the tapes and renamed them, etc. Retrospect goes to a lot of trouble to make sure you don't lose your data. Sometimes it gets annoying.

 

From that point on, he just did "Normal" backups. Based on what you reported, he probably has three backup sets, one for each library. When he moves out a library and moves in a new one, he switches the backup set destination to match the inserted library. Or perhaps he has done this by an appropriate schedule. Or perhaps he always leaves all three backup sets scheduled all the time, and two fail each day because their tapes can't be found. No way to tell without seeing his schedules and procedures.

 

Regardless, Retrospect knows what is on each of the backup sets (libraries), and does the right thing, backing up what is needed for that backup set to bring it current. It doesn't erase the backup set unless you explicitly instruct it, and, even if the backup set is erased (recycled), it will back everything up the first time so that the snapshot is complete. Because your backup person said that he wasn't doing full backups at the start of the week, I assumed that the old backup sets were being put back in, unerased, and Retrospect will just do the right thing.

 

Clear?

 

Here's the manual:

Retrospect Mac 6.x Users Guide

 

I suggest that you study it so that you can get your head around the Retrospect paradigm. Of course, additional information is backed up, too (metadata - permissions, dates, etc.).

 

The only qualification on the comment that a restore can be done is that the selectors be set right to choose the files to be backed up. If, for example, he is only backing up files that start with the letter "a" or some such odd selector criteria, then you will only be able to restore those files. I suggest that you do a test restore, or go in and browse the snapshots, to convince yourself. The catalogs (information as to what is backed up) are separate from the tape members, so you can browse the snapshots while the tapes are offline.

 

The learning curve is a bit steep until you grasp the paradigm because it's different from the model presented by other backup programs.

 

Russ

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Thank you for your help. this puts my mind at rest.

 

I was hoping to find the manuals, I actually enjoy looking at them.

 

My last questions would be, how often should one "recycle" the tapes

and if in the worse case, would Retrospect have to go through all three libraries (assume he has not recycled the tapes in a while) to do a recovery?

 

 

Thanks

 

Bob

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Quote:

My last questions would be, how often should one "recycle" the tapes

 


Well, as a consultant, you must know that there is no "one size fits all" answer. It depends on your backup policy. One consideration is accessibility on restore. Another is reliability (life) of the tapes, which is a tradeoff between tape cost and value of the data. If a tape breaks, the data on that tape can't be recovered. If a section of a tape wears out and becomes unreadable, that data is lost. Another consideration is the nature of the data (transient vs. persistent).

 

For example, ours is a patent and trademark law firm, and our data is valuable. Retrospect (and our offsite tape storage) saved our butt when our floor of our office building burned down a couple of years ago. Patent cases have a life of 20 years. Trademark cases can last forever. We never reuse tapes, and our backup set size (number of tape members) is chosen such that we have to periodically start a new backup set (put a new set of tapes in the autoloader) at some interval. The autoloader holds two backup sets, with backup to alternating sets each day, and we rotate one set off-site each week, never to return. We can go back to the state of any computer on any day for the past 15 years.

 

We don't reuse tapes because our fear is that some file might be inadvertently deleted and the deletion might not be discovered for a year or two (or five), when we reopen the case for some reason. But our situation and needs might be different from your client's. Here's a good discussion of the issues to consider:

What should a good backup policy address?

 

Quote:

and if in the worse case, would Retrospect have to go through all three libraries (assume he has not recycled the tapes in a while) to do a recovery?

 


You haven't provided enough facts to answer that. It's unclear whether the libraries are separate backup sets, but I suspect that they are. If so, then each backup set (library) stands alone.

 

Additionally, as you recognize, if one library is in for a week, then removed and replaced with another, and then replaced with another, and a transient file is desired that was on the first library, then deleted while the second library was in, etc., that file won't be found on the second or third library.

 

If you are doing a "full restore", Retrospect might have to go through all of the tapes in a backup set (library) to catch all of the files. But it's possible that your data is very transient, and all files will be on the last tape in that library. Retrospect doesn't scan the library to find the files; it scans its catalog (kept separately) for each backup set, and then goes to the particular tapes it needs in order to do the restore. If only a single file or a few files are needed for restore, it will go directly to those tapes (for each library) and ask for the operator to insert the right tape if it can't find it already inserted.

 

Clear?

 

Russ

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The firm sells art images. The files are large and static, with new files added on a daily basis. As with your patent example all of the files are important though they do not change after being created.

 

It sounds to me that he did a recycle on only one library and they just continuously rotate through the three libraries. I meant to ask, but forgot to ask, how often they retire tapes. It seemed to me they do not every retire any tapes.

 

I really appreciate this discussion thank you for your help.

 

Bob

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