Am I using compression - how to verify

[Thomas_Olsen]

Hi All

Just to give you a brief background for my question.

In March this year, I changed from a Ultrium1 (MSL 5xxx) to Ultrium2 (MSL 6xxx) on my tape technology.

Every month I do a duplication of the last week's full backups to store offsite.

Before changing technology the duplication was 6-7 tapes.

When changing technology I was thinking that since I basically double the capacity per tape each duplication should be no more than 4 tapes.

I was pretty surprised to discover that duplications still ended up on 7 tapes after running completely on Ultrium 2.

The data volume increase since the Ultrium1/2 swap is very close to zerro.

My question is as follows:

Is there a way I can check if compression is actually being performed during backup?

I am running NetBackup Enterprise v6.5.1 on a Windows 2003 Server SP1.

I have verified (in device manager) that I am using Symantec tape drivers and I don't see any errors in the system at all.

Some help is greatly appreciated.

/Thomas

[Dion]

Not sure if you can check if hardware compression is on from NetBackup - you can check for NetBackup's software compression (try not to use this feature).  You should be able to use the library/tape management tools/interface to check whether compression is set on for your drive units.

Just a quick question... Are your +-8 new LTO2 tapes getting filled up?  If you are running multiple tape drives, you might just find that you are running e.g. 4 streams (1 to each tape) at a time.  This could potentially end up costing you 4 x unfilled tapes.  You can then multiply this by the number of media servers you have running (if you aren't using the new Server Group option in version 6.5 which allows for media sharing.

If you are running 6.5+ you can also set the maximum partially filled media option for the volume pool.  If you set the option for e.g. to 2, you will get a maximum of 2 partially filled media in a given pool.  This will also restrict the number of write drives down to 2.

If you are using an older version of NetBackup you could also restrict the number of concurrent write drives on the Storage Unit (time permitting) which will also restict the number of drives that can be written to at a time for that storage unit.  This will however increase the amount of time taken to do the duplication.

Cheers

[Thomas_Olsen]

Hi Dion

Thanks a lot for your feedback.

I will take a look at the Library & Tape Tool (if that's what you refer to) once I get to the office tomorrow, to see if I can find any information regarding compression.

I am honestly not 100% sure where in NetBackup I can see if a specific tape is filled up or how much remaining free space. Any advice there?

My MSL6060 only has two tape drives with one single Master Server (no media servers). During a duplication, one drive is used for reading and one for writing, so I don't think I have a lot of half full tapes in my duplication.

The Maximum Number Of Partially Full Media option for this particular duplication pool was set to 0 (meaning no limits). I changed this to 1 so we'll see if that makes a difference during my next month's duplication (even if I don't think it will make a difference).

Regards,

Thomas

[Jim_Miller]

I meant this post to be a reply, but somehow it ended up as a new thread.

https://forums.symantec.com/syment/board/message?board.id=21&thread.id=44717

[Dion]

We are using an MSL6060 in our test environment (I sat up till 2am this morning getting it configured!).  Jim is correct, you can just connect to the admin web interface and log in with the the, highly secure, password of 2.  Select the link to manage the library and you will see the tape drives at the top, with all the media below and then information about the library and drives below that.

Our library has 3 x LTO3 drives has the Fibre - SCSI bridge installed - it's a pain as I could not get NetBackup to see each of the tapes in the proper order.  NetBackup always maps it's drive 1 to HP's drive on ID 1, drive 2 to HP's drive on ID 2 and drive 3 to HP's drive on ID 0 - real bugger!

Cheers

[Dion]

Sorry, about checking whether a tape is full.

Select Media in the NetBackup Administration console.  Customise your column to include all the columns you want.  I think the one you are looking for is something like media status which will show whether a media is Active, Suspended, Frozen, Full etc.  You will notice that, depending on the type of data you back up, the compression ratios will change.

e.g.
When I was using LTO3 on the MSL (400GB - 800GB with compression), I would get anything between 450GB up to 1.1TB (on rare occassions!)

Originally, I was using about 8 tapes a night and was only backing up 1.5TB on weeknights.  I managed to reduce this to around 3.

Cheers

[Thomas_Olsen]

Dion / Jim

Thanks again for your feedback.

I checked the web interface of my MSL 6060 library, but I don't see any information about compression ratio. I noticed that you have SDLT drives, while I have LTO2 drives.

As for my 9 tapes used for duplication this month, the Media Status column shows "Full" for 7 of them and "Active" for the last 2.

I am backing up 16 servers using this system. To get some figures on the total amount of data backed up, I logged in to each server and checked disk space used in Windows explorer.

The total disk space used was just above 1TB.

Considering this amount of data, I should be able to almost fit it on 5 tapes even without any compression at all.

/Thomas

[Dion]

From the MSL management interface, you can only check whether hardware compression is on or off. There is no way of knowing what the compression ratio is going to be until you calculate how much data is on a Full tape.  Keep this in mind, compression on zip files will be way worse than on text files.

You can add the Kilibytes column under the Media section to see how much data is actually written to each tape.  You will notice that the amount of data on each tape will be different (because they will get different compression ratios depending on the type of data being backed up).  If you add all these figures you should match fairly closely the amount of data that you are backing up.

Check the following

Make sure that the tapes you are calculating do not contain more than one days worth of data.

Make sure that you are not backing up the same data more than once. e.g.

    doing an OS backup of all the data and then doing an Exchange or SQL backup.  If so you should exclude the Exchange or SQL flat database files

[Dion]

Sorry, I hit the tab and space key and the previous post was submitted incomplete but should be enough to get you started.

Cheers

[Thomas_Olsen]

Hi Dion

I was able to verify from the MSL web interface that compression is turned on.

With regards to adding up the Kilobytes column, I need to wait and calculate all my full backups in order to get the complete picture.

Regarding total backup size, I ran a Client Backups report and added up the full backups (File backups, SQL backups and Exchange backups). I ended up with 661254127 KiloByte which should be about 630GB compressed on the tapes.

I just find it more and more strange why it spreads out on 9 tapes.
Tapes used for duplication are picked from the Scratch pool, so they should all be enpty.

/Thomas