lynnbecker Posted February 21, 2012 Report Share Posted February 21, 2012 I thought I had seen something on this before, but now I can't find it so I apologize for asking again. Once you've set a backup set as uncompressed - which in our case uses a lot more tapes - can you turn on compression for the same set? Or can you not mix compressed and uncompressed files on a given backup set? thanks. Quote Link to comment Share on other sites More sharing options...
Lennart_T Posted February 21, 2012 Report Share Posted February 21, 2012 There are three types of compression, which one do you refer to? 1. Compress the catalog file. 2. Software compression of the contents of the backup set. Usually disabled for tape media sets. 3. Hardware compression in the tape drive. I think that is quite hard to turn off. Are you sure you have HW compression turned off? Quote Link to comment Share on other sites More sharing options...
lynnbecker Posted February 21, 2012 Author Report Share Posted February 21, 2012 I'm actually talking about the option in the Retrospect Options window, where you have a checkbox for Verification, and another for Data Compression (in software). Thanks again. Quote Link to comment Share on other sites More sharing options...
Lennart_T Posted February 21, 2012 Report Share Posted February 21, 2012 That checkbox shouldn't be needed for tape backup sets, as the compression takes place in the tape drive. If you look at the members in the tape backup set, how much is stored on each tape (at most)? How much capacity are there on each tape, according to the manufacturer, EXCLUDING compression? (Manufacturers often assumes 2:1 compression when they state tape capacity. With (very) fine print, they state the actual capacity.) Quote Link to comment Share on other sites More sharing options...
lynnbecker Posted February 21, 2012 Author Report Share Posted February 21, 2012 I guess the question is not whether or needed or not, but whether anything bad will happen by turning on the checkbox for a backup set on which the original and previous incremental backups had it turned off. It does seem to make a difference as backups that fit on four tapes before are now requiring six or more. Quote Link to comment Share on other sites More sharing options...
Lennart_T Posted February 21, 2012 Report Share Posted February 21, 2012 Well, if something bad happens is depending on the answers to the questions I asked above, and some new ones below. What kind of tape drive do you have? Have you ever cleaned it? What kind of tapes? Quote Link to comment Share on other sites More sharing options...
twickland Posted February 22, 2012 Report Share Posted February 22, 2012 That checkbox shouldn't be needed for tape backup sets, as the compression takes place in the tape drive. Some (especially older) tape drives do not offer hardware compression, so software compression can be helpful in these cases. If the tape drive does provide hardware compression, Retrospect automatically disables software compression. I'm pretty sure that Retrospect 6.x can handle backup sets where some of the data is compressed and the remainder is not (I seem to recall our having done this in the distant past). To verify this, I would create a test backup set in which you turn on compression after writing some uncompressed data to the drive, and then confirm that you can restore data from the backup set. Quote Link to comment Share on other sites More sharing options...
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