Duplicate Job Compression

[TR-BE2014]

I'm backing up to a dedup device, then have a duplicate job to back it up to tape. I understand that I can't compress data in a duplicate job after it has already been compressed, but here's what I don't get. Deduplicated data is reduplicated when it is transferred off of the dedup device, so at that point it is not compressed in any way. Why can't it be compressed to tape at that point?

Also, this may be a moot point, but why is the hardware compression option available for the duplicate job, but software isn't?

[CraigV]

I would say because compressing data that is being decompressed is probably going to give you terrible performance, and simpoly not allow you to duplicate to tape in any reasonable amount of time.

At least using hardware compression takes the load of the media server that is already going to be loaded heavily by the duplicate process.

Thanks!

[TR-BE2014]

Sorry, I should clarify - the hardware option only works if available, and apparently it isn't for duplicate jobs (despite the dropdown box being there). The drive hardware compression was enabled by default when I installed everything and has worked for jobs that go straight to tape.
 

[VJware]

The duplicate copies the source data as it is. So, if the original backup set is software compressed, the duplicate will also be software compressed (even when this option isn't present in the UI) and if the original backup set was not compressed, the duplicate backup set will also be not compressed. We don't support when the original backup set is not compressed and the duplicate is software compressed. Hence, the software compression was removed from the UI for the duplicate (i guess, couple of versions back).

Hardware compression should work for the Duplicate jobs. Have you run a scsi trace to check if compression is being or or off ?

[CraigV]

...probably has to do with compressing data as it is being rehydrated. I don't think this will be possible for dedupe data.

Normal B2D data should compress just fine when being duplicated.

Thanks!

[TR-BE2014]

Thanks, all.

VJware, I'll run a scsi trace and see what I get. Any particular options to choose?

[VJware]

This KB should help - http://www.symantec.com/business/support/index?page=content&id=TECH50960

Pretty sure hardware compression for duplicate jobs work, but let me double-check w.r.t. DeDupe source backup sets.

[TR-BE2014]

OK, I ran the scsi trace using the first few seconds of the actual job that didn't compress. I'm attaching the relevant events, but the short story is:

Event 1014 - Mode_Select6 shows the compression set

Event 1015 - Mode_Sense6 shows no compression

Event 1018 - Same as 1014

Event 1019 - Same as 1015

Even 1022 - Write starts

So why would compression be showing up for mode_select but then not for mode_sense?

Thanks.

[VJware]

Apologies for the late reply. Would you pls log a formal support case and then PM me the case number. Thanks.