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Compression

Ayman Altounji
Valued Contributor

Compression

We have a single 35/70 tape drive installed in a Compaq Proliant 3000 server using Novell Netware 4.11. The backup software we use is ArcServeIT 6.6 for Netware. ArcServe states that v6.6 does not offer software compression and that the only way that files can be compressed during backup is if the tape drive supports hardware compression. I am assuming the DLT 35/70 supports compression and have turned this on via the front control panel but I still can't get more than 35 of data on a tape. We are backing up user data files & groupwise stuff. Any suggestions as to what might be the problem. thanks.
1 REPLY
Ayman Altounji
Valued Contributor

Re: Compression

Not much can be done about certain types of overhead, such as directory information, file markers, etc. However, there is one that, like hard drives, can be manipulated: block sizes. Block sizes are defined by the backup software. When backing up large files, this is not a problem. However, when backing up a lot a small files, that can be a problem. Suppose 64K block sizes are being used, and the files stored on a particular volume mostly range between 512 bytes and 16K. Then, with most of the files, at least 64K-16K=48K of space is wasted. That is 3/4 of the space. However, reducing the block size may not be that simple. Every time the block size is reduced by one half, the speed of the backup also is reduced. There was a dramatic effect of using 512 byte block sizes on the performance of the backup. To find the best combination, backup experiments using differnet block sizes may be necessary.