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Re: Data Protector Express Single Server - Data Compression

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Mark Sisley
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Data Protector Express Single Server - Data Compression

We have Data Protector Express Single Server Ver 3.5 SP2. Currently out HP tapes (C7973A) are full at 300GB. (We also excrypt using DPE)

We have the HP StorageWorks Ultrium 920 tape drive.

My question is:
How do I get to the stated 800GB capacity? Do I have to turn off encryption? If I upgrade to DPE multi server, can I get to 800GB & use encryption?
Respected Contributor

Re: Data Protector Express Single Server - Data Compression

Encrypting data anywhere before it hits the tape drive will guarantee that the data is not compressible. If it is important to encrypt your data, either keep using the backup application but turn off compression on the tape drive (since you know the data is no longer compressible), or, use LTO-4 tape drives and media; LTO-4 performs HW encryption without a performance penalty, and compresses before it encrypts, so that you don't lose compression.

Now, the bad news. LTO-3 tapes and tape drives write a "native" 400GB. The 800GB number is assuming that your data is 2:1 compressible. Most user data is *not* 2:1, however; If I had to pick one number, I'd say that most customers tell me their data is about 1.3:1 compressible.

Now, it looks like you're getting less than the native 400GB on a tape. I can think of a few possible reasons for this.
- Compressing in the backup application: if the backup app is encrypting and then trying to compress (a bad idea), it will actually expand the data, because of the metadata it has to store about the compression, even though it didn't work.
- Lots of deeply nested directories and long file names: That file and directory metadata has to be stored on tape with each file as part of the backup process... it's conceivable that this data is significant.

The version of Data Protector Express that you are running has no effect on compression to the best of my knowledge -- it's simply a limitation on the number and configuration of systems you can back up.

I would:
- turn off application encryption and see how much data fits on a tape
- consider running HP Library and Tape Tools, running the disk test and checking for the compressibility of your data.

The only "guaranteed" way to get 800GB on a tape is to use a tape that is at least 800GB native -- be careful with the 2:1 assumption!
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Mark Sisley
New Member

Re: Data Protector Express Single Server - Data Compression

thomasr - I appreciate the information. You confirmed everything I had suspected. One last followup question. I have multiple servers to backup, would you upgrade the single server version or would you go with a completely different package? Keeping in mind I probably will not be replacing the tape drive for a while. Also we are considering starting up sharepoint services sites for subsidiary colaboration.