SCO OS-5.05 / Compaq Proliant Server / Tape Drive Issue

[Mike_489]

Hello all,
I'm having a strange issue with my tape drive (Sony SDT-10000) in a SCO OS-5.05 env't. When i do my nightly backups, it keeps failing at 23.5 gigs compressed, but that drive should be able to handle 40 compressed.
I've had the tape drive itself changed by Compaq and that didn't change help.

I use Microlite Edge as my backup software and the hw guys blame the sw guys and vice versa.

I wanted to throw it out to you guys incase someone ran into a similar situation before. The tech from Microlite suggested that maybe some files weren't/couldn't be compressed, but what's the point of compressed backups if that's the case. It should be able to handle any type of file.

Thanks in advance and any help is greatly appreciated.
-Mike

[Eugeny Brychkov]

Mike,
if you're backing up compressed files then you can store only 20GB of data (native capacity). If compression ratio will be 2:1, then 40GB, if 10:1 - 200GB :o)
Thus as soon as you're getting 23.5GB then overall compression ratio should be 1.175.
Remember also to turn on only one compression at a time: either software (zipping files, turning this option in backup utility or backing up non-compressable files like mp3 and pdf) or hardware compression
Eugeny

[Dave Dewar]

Hi Mike,

Compression works by removing redundant information from the data while still ensuring that the original data can be restored.

Compression efficiency varies from one compression algorithm to another but there is a limit to how compressible a file is.

If the file has already been compressed by another algorithm such as zipping it, then most of the redundant info has already been removed and so when the file is pushed through a different algorithm as used by the tape drive the file will not compress much more. With some algorithms data expansion can occur.

Try zipping up jpeg grahpics files (compressed graphics format) and see how much smaller you can get the file, not much :-)

Hardware compression is provided on tape drives to provide an easy means to compress the backup image without having to use software compression within a backup application. Software compression can require lots of CPU cycles and can lead to poor performance since the tape drive ends up waiting for the host to finish compressing the data before it is sent to the drive.

Since you are getting 23GB on a 20GB native capacity tape then compression is active and working but it sounds like you data stream is not very compressible.

You can check test the compression ability of your tape drive using the performance troubleshooting guide and tools available from the link below:

http://h20000.www2.hp.com/bizsupport/TechSupport/Document.jsp?objectID=lpg50167&locale=en_US&taskId=110&prodSeriesId=63891&prodTypeId=12169
Cheers,

Dave Dewar.

[Sunil Sharma_1]

Hi Mike,
I think you r tring to take backup of already compressed files and in this case drive will not add any more compression.
It will just dump in tape.

I think your Tape drive is 20/40 GB.

You can try to take backup of more then 25Gb using some other utility like tar, or dd and see wheather it work or not.

Sunil