On Wed, May 4, 2011 at 6:36 PM, Erik Trimble <erik.trim...@oracle.com>wrote:
> On 5/4/2011 4:14 PM, Ray Van Dolson wrote: > >> On Wed, May 04, 2011 at 02:55:55PM -0700, Brandon High wrote: >> >>> On Wed, May 4, 2011 at 12:29 PM, Erik Trimble<erik.trim...@oracle.com> >>> wrote: >>> >>>> I suspect that NetApp does the following to limit their resource >>>> usage: they presume the presence of some sort of cache that can be >>>> dedicated to the DDT (and, since they also control the hardware, they >>>> can >>>> make sure there is always one present). Thus, they can make their code >>>> >>> AFAIK, NetApp has more restrictive requirements about how much data >>> can be dedup'd on each type of hardware. >>> >>> See page 29 of http://media.netapp.com/documents/tr-3505.pdf - Smaller >>> pieces of hardware can only dedup 1TB volumes, and even the big-daddy >>> filers will only dedup up to 16TB per volume, even if the volume size >>> is 32TB (the largest volume available for dedup). >>> >>> NetApp solves the problem by putting rigid constraints around the >>> problem, whereas ZFS lets you enable dedup for any size dataset. Both >>> approaches have limitations, and it sucks when you hit them. >>> >>> -B >>> >> That is very true, although worth mentioning you can have quite a few >> of the dedupe/SIS enabled FlexVols on even the lower-end filers (our >> FAS2050 has a bunch of 2TB SIS enabled FlexVols). >> >> Stupid question - can you hit all the various SIS volumes at once, and > not get horrid performance penalties? > > If so, I'm almost certain NetApp is doing post-write dedup. That way, the > strictly controlled max FlexVol size helps with keeping the resource limits > down, as it will be able to round-robin the post-write dedup to each FlexVol > in turn. > > ZFS's problem is that it needs ALL the resouces for EACH pool ALL the time, > and can't really share them well if it expects to keep performance from > tanking... (no pun intended) > > On a 2050? Probably not. It's got a single-core mobile celeron CPU and 2GB/ram. You couldn't even run ZFS on that box, much less ZFS+dedup. Can you do it on a model that isn't 4 years old without tanking performance? Absolutely. Outside of those two 2000 series, the reason there are dedup limits isn't performance. --Tim
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