NTBACKUP, Compression and Travan drives 1

[ShackDaddy]

I’ve got a Travan drive (seagate stt3401a) in a client’s server (not recommended or purchased by me) that is supposed to do 20gb native and 40gb with compression. I have a backup larger than 20gb. I checked to make sure that hardware compression was on in an NTBACKUP script, but we’re still topping out at 20gb and dying.

So I look up the manufacturer’s page on the drive, and I see this:

Capacity: Up to 20 Gbytes native capacity using Travan 40 cartridges, up to 40 Gbytes compressed capacity using software data compression.

I figure that the backup software that came bundled with the device can make the cartridge take 40gb, but apparently the basic driver that runs with Windows 2003 can’t. Has anyone here figured out a way to make NTBACKUP use a Travan’s full compression for a job?


ShackDaddy
Shackelford Consulting

 

[nsantin]

40GB is misleading, it really should be "Upto 40GB assuming you are only backing up text files". Most likely NTBackup is compressing, but not very well.

 

[ShackDaddy]

I don't think it's compressing at all. My backup died Friday night at a byte total of something like 20,112,036,911.

I doubt that's even the full 20gb. It's probably as far as it got before one more decent sized file would have taken it over 20gb.

ShackDaddy
Shackelford Consulting

 

[LWComputingMVP]

The built-in NTBackup utility does NOT support software compression. If the hardware does compression, then the hardware will compress the data... but NTBackup is compression ignorant.

Further, you're falling for the hype. Tape vendors LOVE to say you'll get 2x or more the native capacity of the tape. Meaning they SAY you'll get 40 GB on a tape - but in reality, how much you can fit on a tape depends on how compressible the data is. If you are backing up MPG, JPG, ZIP, and MP3 files, you MAY not even get the 20 GB of a native tape (if it's doing hardware compression - when compressing already compressed data, it CAN use MORE space than the files on the drive. If you are compressing a text file that's 400 GB but contains nothing more than the letter "a" repeated 400 billion times, then you'll likely see a compression ratio so high the end result is a 400 GB file takes 12 bytes (depending on the compression used).

The point is, any experienced admin will tell you, DON'T TRUST COMPRESSION to give you the advertised capacity. Plan your backups around the NATIVE capacity of the tape and if you get more, GREAT.