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theboyk

Can Retrospect 9 report hardware compression?

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When I create my LTO-4 Media Sets using Retrospect 9, it gives me an option to enable/disable hardware compression. But, when I enable hardware compression (with no encryption, password protection, etc.,) when I look at the summary for the script that uses a Media Set with hardware compression enabled, it says "Data Compression Off". The only way I can get the summary to display "Data Compression On" is to enable software compression.

 

So, my question — how do I know if hardware compression is actually enabled or not? I'm enabling it in my media set, yet the script summary says data compression is off? And after running the backup, the logs show no information regarding any compression. So, either hardware compression is being disabled (even though it's enabled in the Media Set) or Retrospect just isn't able to display any information regarding hardware compression from the drive?

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When I create my LTO-4 Media Sets using Retrospect 9, it gives me an option to enable/disable hardware compression.

Are you sure it's the hardware compression and not software compression?

 

 

 

So, my question — how do I know if hardware compression is actually enabled or not?

It's on by default, so if you haven't turned it off using a tape drive utility (not Retrospect) it should still be on.

 

You can also perform a backup of (slightly) more than 800GB of compressable data. The native capacity of an LTO-4 is 800GB. If Retrospect requests another tape then hardware compression is off. Note that all video, most audio and all JPEG files are already compressed.

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Yep — 100% sure about the Media Sets creation giving the option to enable/disable hardware compression — that's the only place you can enable/disable hardware compression (same with Retrospect 6). Software Compression is handled elsewhere, in Scripts > Options > Data Compression (Software).

 

That said, enabling hardware compression doesn't seem to make a difference, and if anything, actually makes things more confusing. With hardware compression off, I get a report of 15GB of data backed up and an semi-accurate reading for space free on the tape and tape capacity (~780 GB). With hardware compression enabled, everything goes out the window. The reports for data backed up is identical to when hardware compression was off (15GB — thus, zero compression — should be ~30% compression based on software compression tests), but now the space free and capacity are different (1.5 TB).

 

It just seems broken when dealing with hardware compression — which is no different than what happened with Retrospect 6 (broken).

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As per the updates to my other posts, which all came back to Hardware Compression (hey, Retrospect — you might want to include this in the Retrospect 10 Addendum when you ship the Retrospect 8 User Manual and Retrospect 9 Addendum with Retrospect 10)...

 

 

 

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.

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How Retrospect handles hardware compression has been the same for 20 years.

 

Retrospect is displaying the pre-compressed space used so far. Retrospect has no way to know what the rate of compression is for tape. The tape drive does not report compression rates, so Retrospect can only tell you how much data was copied from the computer onto your tape, not how much space that data is taking up on the tape.

 

This FAQ applies more to Windows, but the concepts are the same:

 

http://kb.retrospect.com/articles/Retrospect_Article/Tape-Capacity-FAQ/

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Thanks Mayoff. Makes sense, just a shame Retrospect is unable to document any of this properly in the supplied "documentation".

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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:

Excellent summary. Thank you. :)

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