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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Jeff Mohler
Tech Yahoo, Storage Architect, Principal
Twitter: @PrincipalYahoo
CorpIM: Hipchat & Iris
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.