Yes the compression directives refer to Software compression.
When NetWorker reports the number of bytes written to a volume, it "counts the number of compressed bytes" written, not the number of bytes represented by the compression. That is, if 100 Mbytes is compressed to 50 Mbytes using compressasm, the number of bytes written to the tape is recorded as 50 Mbytes.
However, if hardware compression is turned on, then the number of bytes written to a tape volume is counted as the number of uncompressed bytes written. The tape drive performs compression on the fly, typically at a ratio that fluctuates from 1.5:1 to 2:1.
So the capacity indicator when using hardware compression is (understandably) meaningless because networker does not have a clue as to how much the data was compressed at the HW level.
Makes sense, but I just don't recall seeing tapes all measuring 100%. I'm going to backup 100GB of data to see if it fits on the tape or not.If compression did occur on the last backup, it will fit, if it didn't compress I will get an error.
I'm half tempted to turn on software compression directives but half expect this software AND hardware compression to be regarded as bad practice.
Daniea3
123 Posts
0
April 19th, 2012 07:00
Hello John.
Yes the compression directives refer to Software compression.
When NetWorker reports the number of bytes written to a volume, it "counts the number of compressed bytes" written, not the number of bytes represented by the compression. That is, if 100 Mbytes is compressed to 50 Mbytes using compressasm, the number of bytes written to the tape is recorded as 50 Mbytes.
However, if hardware compression is turned on, then the number of bytes written to a tape volume is counted as the number of uncompressed bytes written. The tape drive performs compression on the fly, typically at a ratio that fluctuates from 1.5:1 to 2:1.
Regards,
Arun
deaddog
20 Posts
0
April 19th, 2012 08:00
So the capacity indicator when using hardware compression is (understandably) meaningless because networker does not have a clue as to how much the data was compressed at the HW level.
Makes sense, but I just don't recall seeing tapes all measuring 100%. I'm going to backup 100GB of data to see if it fits on the tape or not.If compression did occur on the last backup, it will fit, if it didn't compress I will get an error.
I'm half tempted to turn on software compression directives but half expect this software AND hardware compression to be regarded as bad practice.