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Tape member actual usage issue


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When i check the members of a backup set they show actual tape usage/capactity at around 100gb. Our tapes are VXA X23 that support 160/320gb and 80/160gb. Is there something in retrospect that I need to change to allow it to maximize the amount of data that can be written?


(the data rates are based on a matched drive that can store at the capacity which we also have in conjunction with retrospect)




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Retrospect uses the tape until EOT. Actual tape capacity depends on the speed of your computer and I/O subsystem (how fast Retrospect can pump data to the drive), on the compressibility of your files, and whether your file mix is lots of small files or only big files.


X23 tapes only support 160/320 GB on VXA-320 drives; you don't say whether you have VXA-2 or VXA-320. Once a tape is written as VXA-2, it will continue that way when used on a VXA-320 for backward compatibility unless you erase the tape (there's a header that the drive lays down that marks the type of tape). And the rated capacities (160/320 GB or 80/160 GB) are marketing numbers for best-case situations (high-compressibility files, big files, fast computer and I/O subsystem).


We've got an Exabyte VXA-2 1x10 1u PacketLoader (SCSI, attached to ATTO UL4D) and we see about 115 to 120 GB capacity on our X23 tapes using Retrospect Mac on our Xserve G5, so your capacity seems about normal.


There is a setting that can be set using Exabyte's vxatool to choose "maximize capacity" or "maximize speed". I don't know if Retrospect leaves this setting alone or whether it sets it one way or the other, but there's no preference setting for it. You might try setting that to "maximize capacity" using the vxatool and see if things change. The drive will also lower the density (increase VXA packet spacing on the tape) if the computer cannot keep up with the drive's data needs, so that the tape doesn't have to back up after stopping when data is not there when needed.



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