Tape capacity vs. actual written data

[ottm]

Being somewhat new to Arcserve, I have a problem I can´t quite figure out.
I´m using tapes with 24GB capacity.
The job is a combination of normal files, registry files and exchangeDB.
I am backing up with data compression.
This is what happens:
When the job has written aprox 10GB of compressed date, the tape seems to be full, and Arcserve request a new tape to continue. At one specific job, which was able to complete, I saw that it had taken 11.6GB of files, 0.3 GB of registry files and 4GB of exchangeDB, and written it compressed as a total of 10.5GB, notyfing that remaining tape capacity was 737MB. (a total of 76614 dir´s, 229316 files and 57 DB/TLogs)

Conclusion: A 24GB tape can only hold 11GB of data??????

I have 9 dfferent tapes for handling this job, 1 for each day + 2 for odd and even week + 1 monthly. I get the same result for all the tapes being used.

When readying the tape for backup I only perform a quick-erase rather than formatting the entire tape. Could that be part of the problem?

Since the job is run by night, there is none in the office to handle changing the tape, so I REALLY need to get all the data in to ONE tape.

Any advice is greatly appreciated.

Magnus

 

[KevHF]

Some tapes have there 'virtual' data capacity written in bold easy to read lettering and there 'native' (ie real'ish') written smaller and less easy to see.
I do not know of a 24Gb tape but I do know of lots of 12Gb tapes that advertise themselves as 24Gb. They can do this because they are stating the 'potential' of the tape assuming a highish compression rate.
As all of us in IT know you can compress a text document hugely so a 10Mb text file may compress down to just 1Mb and therefore you could get 120Gb of text files onto one 12Gb tape. Great. But you cannot compress programs. So a 10Mb program takes up, well 10Mb of tape - ie no compression possible.Boo! Tape manufactures advertise what they beleive is an average compression ie 2:1 with mixed data, but every company and server is different. My experience is around 1.5:1 but I have got a server that gets less than 1:1 because of the way data is stored on a disk to that of a tape (blocking etc).
It may be that the only way you will get a full backup onto one tape is to buy a tapedrive/tapes with a higher capacity.
It could be that compression is not turned on - but it usually is by default.
Best of luck

 

[tapemeister]

Sometimes if you do reformat the tape and check the compression rate of your drive beforehand, can tweak it up a bit.

We use 40GB DLT tapes that boast 80GB capacity. I have seen for some of my backups getting 200GB per tape with a 5:1 ratio. Again file type has a lot to do with it.

Another thing that needs to be taken into consideration is block size. On AS2K, it is 64K and on our older AS6.1 it was 16K.

If your company can afford it you may consider purchasing a tape library. This is what we use. It will hold 7 tapes.

Good luck!

 

[DebiJo]

You might want to check the list of Arcserve supported tape drives. I recently ran into trouble with some of our Travans. They boast 10/20 gb. However, Arcserve does not support compression on this particular drive. Other Travan's yes, just not mine. Bummer.

http://support.ca.com/techbases/as2000/arc2000.html

Good luck,
Debi

 

[ptrigueira]

Hi.
I'm experiencing th exact same problem, but I know litle about ARCServe. Can anyone help me pointing me to some manual of it?

Tks!

 

[joearcnerd]

The problem is databases. They are already compressed. We were using compaq tapes that say they can get 70g per tape and when backing up regular nt data files we were getting about 90 +/- gigs per tape. But when we went to backing up lotus notes database files, we could only get 40g per tape. After days of over the phone conversations with ca support and getting nowhere, I talked to a compaq rep. who layed it out for me and explained it well. Since the database files are already compressed, they cannot compress anymore and the tapes that say they can get 70g maximum per tape are talking about how much data there is before compression that actually gets put on the tape. Since you are backing up exchange db files this will happen. We changed to SDLT drives which for lotus notes gets an outrageous amount of data per tape and runs much faster backing up. We were getting approx. 330 mb/m on the dlts and now approx. 720 mb/m on sdlts. We are much happier now!