With tapes you have the option of using software or hardware compression or none
at all. I have been using software compression several years expecting that this
was the wisest to use.

I have now been through a period of rebuilding my system due to a disk breakdown
and that has meant a lot restores of mainly small amount of data. These restores
have all taken a very long time to complete from when the tapes were mounted to
the actual data was restored. I can see that bacula knows from the catalog in
which tape file the data may be found. I assume it's very fast to go to the
target file using forward space file, but what goes on when it then locates the
data file within the tape file? I believe it's done by a sequential search of
the tape file. I can see from the tray monitor that it reads block after block
before the restore takes place. This seems to cost a lot of time especially if
the blocks have to be unzipped. If this is true a better restore performance
will be obtained with uncompressed tapes or even with hardware compressed tapes
because here the data is decompressed in flight.

If all this is true I tend to believe that hardware compression is by far the
best method. On the other hand I know that software compression is advocated by
folks more knowledgeable than me.

Would someone please explain what's up and down with this sort of performance?

Thanks,
-- 
Erik.

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