ZFS obn FreeBSD hardware model for 48 or 96 sata3 paths...

[Bob Friesenhahn]

On Fri, 16 Sep 2011, Jason Usher wrote:
>
> So I will boot of a pair of mirrored SSDs formatted UFS2 - easy.  
> But I would also like to spec and use a ZIL+L2ARC and am not sure 
> where to go ... the system will be VERY write-biased and use a LOT 
> of inodes - so lots of scanning of large dirs with lots of inodes 
> and writing data.  Something like 400 million inodes on a filesystem 
> with an average file size of 150 KB.

150KB is a relatively small file size given that the default zfs 
blocksize is 128KB.  With so many files you should definitely max out 
RAM first before using SSDs as a l2arc.  It is important to recognize 
that the ARC cache is not populated until data has been read.  The 
cache does not help unless the data has been accessed several times. 
You will want to make sure that all metada and directories are cached 
in RAM.  Depending on how the files are used/accessed you might even 
want to intentionally disable caching of file data.

Are the writes expected to be synchronous writes, or are they 
asynchronous?  Are the writes expected to be primarily sequential 
(e.g. whole file), or is data accessed/updated in place?

Bob
-- 
Bob Friesenhahn
bfriesen at simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/