[illumos-Discuss] SSD vs "hybrid" drive - any advice?

[Erik Trimble]

On Thu, 2011-07-21 at 15:21 -0400, Gordon Ross wrote:
> I'm looking to upgrade the disk in a high-end laptop (so called
> "desktop replacement" type).
> I use it for development work, runing OpenIndiana (native) with lots
> of ZFS data sets.
> 
> These "hybrid" drives look kind of interesting, i.e. for about $100,
> one can get:
>   Seagate Momentus XT ST95005620AS 500GB 7200 RPM 2.5" SATA 3.0Gb/s
> with NCQ Solid State Hybrid Drive
>   http://www.newegg.com/Product/Product.aspx?Item=N82E16822148591
> And then for about $400 one can get an 250GB SSD, such as:
>   Crucial M4 CT256M4SSD2 2.5" 256GB SATA III MLC Internal Solid State
> Drive (SSD)
>   http://www.newegg.com/Product/Product.aspx?Item=N82E16820148443
> 
> Anyone have experience with either one?  (good or bad)
> 
> Opinions whether the lower capacity and higher cost of
> the SSD is justified in terms of performance for things
> like software builds, etc?
> 
> Thanks,
> Gordon

Gordon,

You'd be better off asking this question on zfs-discuss at opensolaris.org,
where most of the ZFS folks still hang out.

IIRC, the last time we talked about experiences with hybrid drives, it
was pretty clear they were doing solely read-caching with the NAND, so
ZFS would derive no benefit from using one as ZIL vs a standard HD.  The
NAND is completely internal to the HD, and thus, there is no way for ZFS
to take specific advantage of it in any form. 

Write speeds of SSDs aren't any faster than that of Hard drives in terms
of throughput; however, they can generally handle an order of magnitude
greater IOPs, even on writes, so compiling should be noticeably faster
(screamingly faster reading, somewhat faster writing, of lots of small
files). In your scenario (compiling), I don't see the hybrid HD's cache
being particularly useful vs a standard HD - you're doing a large number
of reads across a very large number of files, so I would expect that the
hybrid's NAND cache experiences a rather high rate of eviction, which
reduces its utility greatly.  And, there's no write benefit, so
compiling output to the hybrid will be just as slow as a normal HD.

I'd go with the SSD. Generally, the newer SanForce2 or 3-based internal
controllers seem to be a good bet on any SSD, so look around the Net to
see if the particular SSD you're interested in uses a SanForce2/3
integrated chip. 

-- 
Erik Trimble
Java Platform Group - Infrastructure
Mailstop:  usca22-317
Phone:  x67195
Santa Clara, CA
Timezone: US/Pacific (UTC-0800)