cmcfarling Posted July 25, 2003 Report Share Posted July 25, 2003 We're using a VXA-2 Firewire drive with Retrospect Desktop 5.0.238 and V23 tapes. These tapes are spec'd to hold 80GB of non-compressed data and 160B compressed. Of course, no one ever gets the 2:1 compression ratio that all tape drive manufactures market, so I would never expect to fit 160GB of data on a tape. However I would expect to get more that 80GB due to the fact that the data is going to be somewhat compressible. My question/problem is this... Sometimes we are able to cram 98 or 99 GB onto a single tape but other times the drive claims the tape is full if it has 79GB on it. Could this have something to do with the way Retrospect writes to the tape? Could it have something to do with the fact that it's a Mac Firewire drive? Is it "just the way it is"? I'm just wondering if anyone has some insight into why this might be. I just downloaded the latest RDU (v 3.6.106) which I'm going to install and see if makes a difference. Link to comment Share on other sites More sharing options...
natew Posted July 25, 2003 Report Share Posted July 25, 2003 Hi, My quess is that you are using hardware compression? The advantage is that it is faster. The disadvantage is that it compresses all of the data that is sent to it regardless if it is compressed or not. Compressing a compressed file can actually make it grow in size a bit. As an experiment you could try using Software compression in Retrospect and see if you get better results- it is slower but it also makes choices about which files should be compressed. You can only turn off hardware compression when you create a new backup set. There is also an element of "thats the way it is" to this. Nate Link to comment Share on other sites More sharing options...
cmcfarling Posted July 28, 2003 Author Report Share Posted July 28, 2003 I'm wondering how much capacity is being used up by snapshots. Does anyone know how to determine how much space a snapshot consumes? Link to comment Share on other sites More sharing options...
AmyJ Posted July 28, 2003 Report Share Posted July 28, 2003 For capacity issues on the VXA-2 drive, please see the following Exabyte article: http://www.exabyte.com/support/online/kb/display.cfm?id=1022 Link to comment Share on other sites More sharing options...
ericmurphy Posted July 30, 2003 Report Share Posted July 30, 2003 Here's another suggestion, which works for VXA-1 drives, so I'm assuming it works for VXA-2 drives as well. There's a command line utility available from Exabyte called vxatool (there might be a different version of the tool for VXA-2 drives; check their website). The tool allows you to access a hardware switch on the drive that optimizes the drive for either speed or capacity. I believe the syntax is: ./vxatool tape1 -P S for speed ./vxatool tape1 -P C for capacity I have a VXA-1 drive, and the drive seems to have shipped optimized for speed. I can't say for sure how much difference it makes yet, but optimized for speed a 33-Gig tape held like 33.8 gig of data. So far, with the drive optimized for capacity, it's definitely holding more data. It can't hurt to give it a try. Link to comment Share on other sites More sharing options...
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