Okay, I heard back. Engineering says that snapmirror and vol-move should BOTH trigger compaction. If you didn't see savings, perhaps something about thin provisioning was not configured.
The savings could have been there, they just weren't visible if the volume settings weren't correct.
I would guess that snapmirror is currently looking at the physical blocks on disk, whereas a vol-move is a step up the chain and it can look at block that are actually a block within
a block.
I'll check with engineering and report back...
My understanding is that both are block based operations so it makes sense to me that the blocks would be put down on disk unchanged. Perhaps it has something to do with the fact that you may want to reverse the snapmirror back to the system that presumably
does not have compaction enabled or support the feature, so the blocks are left uncompacted? If the vol move is within the same controller AFF the lack of backward compatibility is not a concern. Just a though, I don't know.
Strange how compaction appears to work with vol move but not with snap mirror.
A vol-move operation will cause compaction to happen. I know it's not ideal but at least its internal. Obviously a scanner is preferred but functionally it would be a lot like a vol move.
Likewise if you use FLI to import a LUN that will trigger all the efficiency features during the import.
Sent from my mobile phone.
Compaction in our testing can be good, really good...an additional 20% in many of our test data sets on top of everything else. (SSET diagnosis)
However, there are limitations on how you get data into AFF to get compaction...IE, you cant snapmirror it.
It must transfer, as far as we're told today, via a host/file based migration. Be thinking bout this when you consider an AFF migration. It must be done outside on ONTAP.
We have pushed to get this fixed via a scanner/etc that reads and relays out the file based structure.
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my sales guy basically said the guarantee works as follows - they don't hit the 4:1 target, they buy you whatever amount of shelf\ssd required to makeup shortfall.
The magic has to do with what they call "compaction" - writes <4KB (down to 512B/ea) are "compacted" into a single 4K block... this apparently adds to the std dedupe and compression they use.
Sales guys are promising me 4:1 dedup ratios on an AFF with ontap9. They say they grantee it. I have specifically asked what stipulation. In a VDI environment with linked clones, etc. Sales guy tells
me none and even specifically says they can dedup compressed video or audio (mp3) 4:1.
I have A LOT of trouble believing that. So, 4:1 dedup guaranteed or what?
Any comments welcome.
--Jordan
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