Log In

Come Join Us!

Are you a
Computer / IT professional?
Join Tek-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Tek-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here


Different compression ratios

Different compression ratios

Different compression ratios

We use a Quantum tape library and Sony DLT IV tapes to back up our data. I've noticed that say nearly all the tapes will have a different compression ratio. Even on our full backup jobs, which span multiple tapes, the compression ratio varies. Eg, for our full Netware backup, the first tape might have 45GB on it, the next might have 60GB on it and the next may have up to 90GB on it. Is there a reason for this?


RE: Different compression ratios


Jason, I suspect the issue is that the files on the server is dynamic.  You may have the server set to compress files - probably yes, perhaps after a week on inactivity.

Now, let say you backup an active area - the files will be uncompressed, and the compression rate will be high.

Then the tape hits large sections of the volume that is very static - read-only documents, program files, etc.  These files have been compressed already -- you will not be able to compress then further - compression ration will be high.

Another situation is backup up encrypted files, or an email database - these files can also not be compressed.  If your backup hits a large ccMail or Lotus Notes database, it will chug along at a very slow rate with no savings.

Perhaps the worst situation I encounter is when I backup a huge number of very small files (FTP copy program) - half the time of a our backup is spent archiving this section - small encrypted PDF files have a relatively poor compression, and require a zillion open / close I/O activity which is deadly.


Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Tek-Tips Forums free from inappropriate posts.
The Tek-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Tek-Tips forums is a member-only feature.

Click Here to join Tek-Tips and talk with other members!

Close Box

Join Tek-Tips® Today!

Join your peers on the Internet's largest technical computer professional community.
It's easy to join and it's free.

Here's Why Members Love Tek-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close