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HP DLT vs80 tape

Regular Advisor

HP DLT vs80 tape

Hi all,
In our setup,DLT vs80 drive is connecting in windows server.Out of 80 GB data catdige,dlt vs80 is used only 50GB space and remaining 30 gGB is not utilized.
Pls tell me how to use 80 GB fully in our vs80 tape drive.I am getting this problem in last one week back.

Russell C. Smith
Valued Contributor

Re: HP DLT vs80 tape

Hi Suresh,

Here's some important information about the DLT VS80 tape drive (and tape drives in general). The quoted capacity for the VS80 is 40GB **native**, 80GB with 2:1 compressible data. 2:1 compressible data means data that can be reduced in size by a factor of two and thus stored in half the required space. If you are backing up absolutely incompressible data you won't be able to back up more than 40GB of data because the data cannot be compressed. If you are backing up data that can be compressed by a factor of 3 then you could very like see the VS80 backing up up to 120GB. Both the tape drive, as well as your backup application, have compression "engines" within them that perform this action on data to be backed up.

Given that you're only able to backup 50GB it may be that your data has a compressibility factor of 50/40 = 1.25. However, it's also worth checking that you don't have both your backup app software compression and your VS80 hardware compression both on at the same time because compressing twice could actually increase, not decrease, the size of the compressed data. Also, if you're backing up a lot of data that is already compressed, even before the backup application or tape drive tries to compress the data then you may end up increasing the size of these files (eg. if you try to compress JPEG, MPEG, ZIP, TAR.GZ, etc. files)

In general, the minimum specified amount of data you should expect to be able to backup with a VS80 is 40GB.

Hope this helps.
Jaclyn Rothe
Trusted Contributor

Re: HP DLT vs80 tape

A DLT IV tape for a DLT VS 80 drive ia a 40 native taope and a 80 compressed tape. If you get over 40 GB then you are utilizing compression and are fortunate that you have gotten that amount of data on the tape.

Compression is very complicated to determine how much data you willg et on a tape. Cartridges differ slightly from tape to tape and lot to lot... also trace info is recorded in the header and footer of the tape to tell the back up softwre how to use the tape and what length it is etc. Therefor you can lose 25% of the tape to header and footer info therefore will probably never fit 80GB on a 40 native tape.

HP hardware is designed to run with an algorithm calibrated at a 2:1 compression ratio. Throughput, network back ups, drity ddrives, old media, bad blocks, file systems, system performance etc call all cause throughput to drop and thusly compression is worse.

You should attempt to configure your system to do local back ups only and stream data at 40mb/s... make sure the device is isolated ont he SCSI card and the recommended SCSI HBA is being used. Ensure drivers are not corrupted and up to date, and make sure back up software is at the latest service packs.

Also software compression is not usually as efficient as hardware compression. We advise using job properties to specify you want hardware compression only. Any selection mentioning software compression or no compression may cause negative results for the compression algorithm on the drive and may result in a poor ratio.

You can typically expect a production back up to achieve 1.4:1 to 1.8:1.

Your data set will also severely affect your compression ratio. Text only files compress remarkably well... video, drawings, picture files are almost always fully compressed and will compress hardly any amount if at all.