theboyk Posted July 4, 2012 Report Share Posted July 4, 2012 Backup #1 Details: LTO-4 tape, regular backup of a ~15 GB folder, no password/encryption, software compression Results: Used = 10.1 GB; Free = 771.3 GB; Capacity = 781.4 GB Backup #2 Details: LTO-4 tape, regular backup of a ~15 GB folder, no password/encryption, no compression Results: Used = 14.8 GB; Free = 766.6 GB; Capacity = 781.4 GB Backup #3 Details: LTO-4 tape, regular backup of a ~15 GB folder, no password/encryption, hardware compression Results: Used = 14.8 GB; Free = 1.5 TB; Capacity = 1.5 TB I set up and ran backup #1 first, wiped the tape, then set up and ran backup #2, wiped the tape, then set up and ran backup #3 — the only difference between the three being software compression vs no compression vs hardware compression. The results Retrospect 9 are displaying make absolutely no sense to me when it comes to Hardware Compression. Backups #1 & #2 seem accurate, but backup #3, with hardware compression enabled, makes no sense. It's showing no compression, but it's also showing about 2x the capacity of the tape? My only guess is, Retrospect is unable to deal with hardware compression since it can't report the information correctly? I mean, if there actually IS hardware compression going on, but Retrospect can't see this information, then it's going to think a tape has reached its capacity before it actually has (then again, it's also showing the tape capacity being double)? Is Retrospect's ability to deal with hardware compression just plain broken? How the heck are people supposed to make a decision on what options to use if the program can't even provide semi-accurate information? I would love to use hardware compression — backups are more than 3x as fast with hardware compression enabled, so I'd be able to have faster backups (vs software compression) AND higher capacity (vs no compression) — but I have absolutely no idea what this is going to mean in terms of the stability of my backups? Will the reporting by Retrospect when using hardware compression correct itself over time (as I know reporting capacity, etc. from tapes isn't an exact science) or will it forever be broken? Quote Link to comment Share on other sites More sharing options...
Lennart_T Posted July 4, 2012 Report Share Posted July 4, 2012 The values for "free" and "capacity" is really useless. The only thing that makes any sense is "used". "Free" and "capacity" assumes that all data can be fed fast enough for the tape drive AND that all data can be compressed 2:1. None of which can be fulfilled in real life. I would also be very interested in learning how you turned off and on hardware compression in Retrospect. AFAIK it isn't possible. Quote Link to comment Share on other sites More sharing options...
theboyk Posted July 4, 2012 Author Report Share Posted July 4, 2012 You enable/disable LTO4 hardware compression when you create a Media Set by either checking or unchecking "Allow Hardware Data Compression" — this is no different than is was in Retrospect 6 and Retrospect 8 (though, I never used it in those versions — actually, I never used v8 at all other than testing it to see if it was worth upgrading to). Assuming Hardware Compression is on, why doesn't Retrospect reflect this? For example, with hardware compression ON, my "used" value is 14.8 GB. With hardware compression is OFF (assuming the Retrospect option to turn it off actually does turn it off?) AND software compression is OFF, my used value is 14.8 GB (the same as when hardware compression was on). But, when hardware compression is OFF and software compression is ON, my "used" value is 10.1 GB (~30% compression). So, what's going on there? If the option to enable/disable Hardware Compression doesn't do anything, why include it? Also, if the option to disable it doesn't do anything, and you also have software compression enabled, then you're double-compressing things, and that doesn't seem right to me? The only thing I see the option to enable/disable hardware compression doing is further confusing the end user, which, apparently, Retrospect UI/UX designers must pride themselves on doing. Quote Link to comment Share on other sites More sharing options...
theboyk Posted July 5, 2012 Author Report Share Posted July 5, 2012 Just an update — I've been going back and forth with Retrospect Support regarding Hardware Compression support and this is what I can confirm, for anyone interested: - Hardware Compression is enabled by default on supported devices (in my case, LTO-4 tape drives). - You can disabled Hardware Compression when creating the Media Set (by unchecking the "Allow Hardware Data Compression" checkbox). - Retrospect in unable to get any data from the drive relating to Hardware Compression. - In both Script Summary and Activities Details, any information relating to Compression being on/off is based on Software Compression. - The only indication as to whether Hardware Compression is on/off is by viewing the Media Set Overview. - When using Hardware Compression, when viewing Media Set details, any information relating to the USED, FREE and CAPACITY values are incorrect; FREE and CAPACITY values are completely inaccurate (so you can ignore them) and the USED value only reports the amount of data that was SENT to the hardware; it does not reflect how much was actually compressed/written since that is unknown (as Retrospect can't get this information from the drive). - The drive determines when a tape is full and reports this to Retrospect (ie. Retrospect does not determine this itself based on USED, FREE and CAPACITY values). - You should not use both Hardware Compression AND Software Compression as this will, most likely, result in the bloating of files beyond the original size (thus, doing the opposite of what you're trying to do). Hope that helps a little. k. Quote Link to comment Share on other sites More sharing options...
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