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DavidHampson
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April 24th, 2009 02:00
Double compression
I've always been told that double compression is something to be avoided with some reasons given being:
* the second compression does not compress any further
* the second compression causes the backup to get bigger than the original compression
* compression places a heavy load on the processor of the client
The only time to use client-side compression is on a very slow network link (no data on what makes a link very slow)
We are using client-side compression due to heavy bandwidth utilizations during backups (I have not verified this personally but taken it on word of mouth so far), we have no issues I am aware of with clients being overloaded by backup processing, compression is enabled on all tape drives.
I'm curious about what is truth and what is myth on double compression and also is there anything we should action on our system based on these facts....
* the second compression does not compress any further
* the second compression causes the backup to get bigger than the original compression
* compression places a heavy load on the processor of the client
The only time to use client-side compression is on a very slow network link (no data on what makes a link very slow)
We are using client-side compression due to heavy bandwidth utilizations during backups (I have not verified this personally but taken it on word of mouth so far), we have no issues I am aware of with clients being overloaded by backup processing, compression is enabled on all tape drives.
I'm curious about what is truth and what is myth on double compression and also is there anything we should action on our system based on these facts....
ble1
6 Operator
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14354 Posts
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Posted April 24th, 2009 02:00
Usually this is correct. Obviously there are different approaches and one approach might give you more compressed data than other, but generally speaking this is correct.
This is mostly ok and again depends on how compression algorithm works. If they are the same it would be like zipping what has been zipped already. The compressed file would most probably increase its size. Since HW and SW methods are probably different you can see that as zipping rar or the other way around. Generally this will cause bigger output and in terms of backups occupy more space on tape.
I have seen examples where this is truth and where there was no big impact.