[OpenIndiana-discuss] ZFS with Dedupication for NFS server

[Edward Ned Harvey]

> From: Roy Sigurd Karlsbakk [mailto:roy at karlsbakk.net]
> 
> > With the 8T storage... Add 8-16G ram to your server on top of your
> > baseline.
> 
> I never got around to filling it. Already at about 1.2TB fill, it was dead slow,
> and for that the 8GB RAM should suffice.
> 
> > I'm not sure how to calculate extra ram requirements for l2arc.
> 
> AFAIK, L2ARC will just "add more, slower RAM"...

Sorry, both of these statements are inaccurate.

(1)  Well, I'll drop the subject of 8G being enough ram.  If I say any more about that, I'll just be repeating myself.  So I'll only repeat one part:  8G is not enough if you have dedup and l2arc enabled and expect it to perform reasonably.  I don't even run a laptop with less than 8G of ram anymore.

(2)  L2arc is not simply a slower extension of L1arc as you seem to be thinking.  Every entry in the L2arc requires an entry in the L1arc.  I don't know what the multiplier ratio is, but I hear something between 10x and 20x.  So if you have for example 20G of L2arc, that would consume something like 1-2G of ram.

Oddly enough, just google for this:  L2ARC memory requirements  
And what you see is --- A conversation in which you, Roy, and I both participated.  And it was perfectly clear that you require RAM consumption in order to support your L2ARC.  So, I really don't know how any confusion came about here...  You should be solidly aware by now, that enabling L2ARC comes with a RAM cost.