VXA drive and compression

[mcniel]

I was wondering if anyone could help shed some light on this issue for me.

 

 

 

The VXA-1 drive supports hardware compression and Knowledgebase Article "Data Compression in Retrospect" (http://www.dantz.com/index.php3?SCREEN=kbase&ACTION=KBASE&id=26667) states:

 

 

 

"Retrospect uses a drive’s hardware compression whenever possible,

 

automatically turning off Retrospect’s software compression if necessary."

 

 

 

My question is this: If Retrospect turns off software compression when hardware compression is available, why do I only average about 32MB/min. transfer when software compression is enabled as opposed to the 120MB/min. transfers when software compression is disabled? If hardware compression is always used, shouldn't the throughput be the same regardless of the software compression setting?

 

 

 

My guess is that Retrospect does not recognize the drive's compression abilities and is using software compression which, on an 8500, would cause the abysmal throughput. However, I want to make sure that if I disable software compression in Retropspect to get a higher throughput, it won't disable the hardware compression on the VXA drive. The VXA tapes aren't cheap and I'd like to cram as much stuff on there as possible.

 

 

 

My system setup: VXA-1 firewire drive, Retrospect 4.3 with Retrospect Driver Update v2.5 on a Powermac 8500 with an Adaptec FireConnect Plus firewire card, backing up about a dozen macs over a 100BaseT ethernet network. Hardware compression is enabled on backup sets, no encryption. Hardware compression is enabled in the VXA drive's firmware.

 

 

 

Thanks for any input

 

 

[anwnn]

I don't think that Retrospect actually realizes whether or not hardware compression is turned on. If you specify Hardware Compression when you create the Backup Set, it will simply show you that you enabled it. I don't think Retrospect talks to the drive to find out whether it's enabled or not. I would however make sure you do not enable both Hardware and Software compression.

 

 

 

Also, you may want to check the firmware settings on the VXA drive, to make sure that it is set to favor capacity over speed, or vice-versa, depending on what you want.

 

 

 

I'm currently trying to figure out why the new VXA2 drive I've got, is only getting 80-90GB on the new V23 tapes, with Hardware Compression enabled.

[shadowspawn]

I am fairly certain that there were issues with some older versions of Retrospect not recognising that the VXA drive supports hardware compression, but don't have an URL for you.

 

 

 

Based on your useful empirical evidence, it seems likely you are affected by the issue, so turn off software compression. This does not prevent hardware compression.

 

 

 

The hardware and software compression options overlap a little, but you allow/disallow hardware compression when you create the backup set, and allow/disallow software compression when you create the backup or backup script.

 

 

[phredd]

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My guess is that Retrospect does not recognize the drive's compression abilities and is using software compression which, on an 8500, would cause the abysmal throughput. However, I want to make sure that if I disable software compression in Retropspect to get a higher throughput, it won't disable the hardware compression on the VXA drive. The VXA tapes aren't cheap and I'd like to cram as much stuff on there as possible.

 

 

 

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I think you are correct. I've got a VXA-1 firewire tape drive hooked up to an

 

iMac running OS X 10.2.2 and I've been keeping an eye on what I'm getting

 

on a tape. 32.0 GB has been consistant with only hardware compression

 

enabled. I've got the drive configured (via vxatool) to favor compression, but

 

I don't seem to be getting any. Most files are text and database, so I should

 

be able to stuff a tape and get at least 50 GB onto one.

 

 

 

This is running Retrospect 5.0.238 and using RDU 3.2.104.

 

 

 

I also just checked out my other backup machine - Quicksilver G4 with a

 

firewire VXA-1. I'm getting about 35 GB per tape there. This one has been

 

in service longer and had been doing backups since before Jaguar (OS X 10.2),

 

so I may have been getting compression before I upgraded to 10.2. I'm

 

also running with the same version of Retrospect and RDU as above.

 

 

 

I remember that Retrospect had issues with 10.2, but had thought those were

 

fixed with 5.0.236 and then 5.0.238.

 

 

 

I may take my iMac down to 10.1.5 next week and see what happens.