Multiple sources - copy all then compare all?

[Cygnis]

Hi all,

 

I've been testing the Backup process using multiple sources. Whether I use 'Source Groups' or individually select each source, the following seems to occur:

 

If I have two sources, "Folder A" and "Folder B", Retrospect seems to do the Backup tasks in this order:

 

- Copy Folder A

- Compare Folder A

- Copy Folder B

- Compare Folder B

 

My thinking is that it would be better for the destination media (especially when using tape) if it did it this way instead:

 

- Copy Folder A

- Copy Folder B

- Compare Folder A

- Compare Folder B

 

That way, it is doing all the writing in one pass, then all the comparisons in one pass.

 

Is there a way I can make it behave like that?

 

Or, am I wrong in thinking there is any benefit to doing it that way? (Note that I intend to back up several sources at a time, not just 2. All sources will be local disks, not client machines.)

 

Thanks very much.

[jgowing]

If all the copies and compares can be completed within your backup window, without interfering with any other production processes, do you really care?

 

If however you are squeezed for window, and need to get all the copying done IN the window, and would then like to get the compares done OUTSIDE the window you have a couple of options.

 

1. Full Compare with orignal data.

On your backup script switch OFF Verify in the script options. ( Optionally specify a specific execution engine number. Bear with me . . . )

 

2. Create a New Verify Script, Select the relevant backup set, Schedule the job to start a few minutes after the backup script starts and before it finishes. (Optionally specify the SAME execution Engine Number as the backup.)

 

If you specify the Execution Engines as above the verify will try to run while the backup is running but CANNOT because the execution engine is occupied. The verify will then wait until the execution engine becomes free when the backup finishes and will run imediately after.

 

Of course you could also just schedule the verify to run at any convenient time.

 

Using a full verify will still cause the original data to be read which may interfere with production processes, in which case use the following approach, (My personal favourite)

 

MD5 Hash verify as a separate job:-

 

Check that MD5 checksums are enabled

Config>Prefs>Media>Verification

Disable Verify in your Backup Script

Run your Verification in a separate job using either method described above.

 

The advantage of this is that your source data is not read, and thus production processes are unaffected.

 

Using this technique allows you to use your full overnight window for backup. Verification can then take place during thday without affecting production.

 

See the Manual Chapter 5 > Scripted Verification for more details

or

Help > Automated Operations > Scripted Verify

 

 

See also http://forums.dantz.com/showtopic.php?tid/32369/post/132228/hl//fromsearch/1/#132228 for similar discussion involving tapes and getting them to eject properly.

 

Good Luck

[Cygnis]

Thanks for the detailed response! Much appreciated.

 

I was more concerned about tape longevity/health than workflow interruptions, but I guess they're designed to be written and re-written many times over, so I'm probably just being excessively paranoid.

 

Good to know about the differences between the types of verification that are possible via scripting, too. (For some reason, I thought that a full compare- which is the same as "thorough verification," right?- was only possible at the time of backup. Nice to know that this isn't the case, and also that the MD5 option is a viable alternative.)

 

Cheers!

[jgowing]

No Prob, you're welcome

 

Of course if you were to run a thorough verify at a lter stage you do run the risk of some source data changing and thus giving an error.

 

However since the MD5 hashes are taken at time of backup that problem won't occur with a later MD5 verify.

 

The other cool thing with scripted verify which I fogot to mention is that Retro is clever and knows what it has already verified, so you can just run a verify whenever, and retro will only verify new stuff.

 

Modern tapes esp LTO are pretty robust, but the "dailies' do tend to get a bit more wear & tear, so it is a good idea to cycle new ones into your high use Backup sets. ("New Member" function in Retro )