[geeks] Understanding ZFS performance (maybe) part 2 - NFS performance solved for $100 bucks

[Joshua Boyd]

On Tue, Aug 11, 2009 at 12:14:14AM -0400, Patrick Giagnocavo wrote:
> Joshua Boyd wrote:
> 
> > 
> > You probably don't want to spend the money, but I'd love to see you
> > directly compare this against a flash drive.  Maybe you could look at
> > the OCZ Vertex drives, or even the cheaper (and probably slower) Emphase
> > SATA modules from logic supply (1 gig for $31).
> > 
> > I suspect that the product you did get gives us a good idea how Sun's
> > Logzilla drive would improve things.
> 
> I think that the log is limited by how fast the media can be written to.
> 
> Thus the 24MB/second Sata modules would limit writes, though I guess you
> could stripe them.

Yes, that could limit writes, however does a 4Kb NFS write result in a
4Kb log write, or a smaller log write?  I'm not sure about ZFS.  I know
that NetApp made a big deal about how their logging method was more
space and speed efficient than the usual NFS logging accelerators.
 
> I was confused earlier about SSDs and Sun, because I thought the ZIL and
> the cache code was the same, but now I see that you could have any
> amount of SSDs in front of the disks and as the cache warmed up, reads
> would get faster and faster; and ZIL on SSD could get faster and faster
> as you mirrored then striped the log disks.

And of course, Sun's Logzilla device is flash backed SDRAM (with super
caps), making it even faster than a regular SSD.