New computer build -- Photoshop scratch drive options

Question

It’s been years since I built my last Photoshop computer, so I’m researching what I want to include in my next build.
I may use this computer for some video editing, but for the most part it will be dedicated to Photoshop.  I’m running CS5.  I’ll be stitching RAW images, & routinely editing 500+ MB files.  The configuration I’m closing in on is as follows:
Windows 7, 64 bit
Intel i5 2500K processor
16 GB’s of RAM
One of the soon-to-be released motherboards utilizing the Z68 Express chipset
My question is about the Photoshop scratch drive, & what’s the best current technology.  On my old computer, I originally had a two-drive RAID 0 array, but when the Promise RAID controller started having problems, I reverted back to a single Raptor drive.  I see three or four possibilities for scratch on my new computer:
1) Use a SSD as my scratch drive.  The question I have is about reliability in this application given the large number of sequential read & write operations required of a scratch drive.
2) Build a RAID 0 array with mechanical drives.  Which ones?  I’ve read that the top-rated fast WD Caviar Black drives have problems in a RAID 0 configuration.
3) Just go with a single drive – Anandtech tests show a single WD Caviar Black drive is almost as fast as single VelociRaptor when the data is sequential reads & writes.
4) The new Z68 motherboards will support the Intel Smart Response Technology that can make the SSD become the "Cache of the HDD" to boost up the HDD access speed.  The idea is to use a small cheap SSD as the cache.  This has yet to be proven in a Photoshop environment, & it may run into the same reliability issues I’m asking about in item #1 above.
Can anyone with PS scratch-performance knowledge enlighten me on the current state of affairs?
Thanks,
--Alan

Answer 1

It's my opinion that you want to do all you can to keep Photoshop from having to go to the scratch drive, and when it must it's going to be painfully slow no matter what hardware you have.  This is based on the theory that RAM access is orders of magnitude faster than disk (even SSD) and the observation that Photoshop sometimes writes horrendously large datasets to the scratch drive.
You're doing the right thing, going to 16 GB (24 GB might even be better).  I have 16 GB and for all "normal" work I find Photoshop to be very fast and not go virtual, even after long editing sessions.  In testing, however, I've been able to force Photoshop to go virtual by doing things like:
1.  Processing a 1 gigapixel image (e.g., 32767 x 32767 pixels).
2.  Stitching fairly huge (substantial portion of a gigapixel when finished) panoramas.
In my case I've chosen to use a single mechanical 1 TB hard drive for scratch, and I've watched Photoshop in case 2 above (panos) actually write more than 200 gigabytes of data to the drive.
I recommend paying a bit more for top quality enterprise class disk drives (e.g., Western Digital RE4), instead of consumer models.  They're fast, are built for hard use and much higher reliability, and have additional features (like vibration reduction).
Also keep in mind that a RAID setup effecitvely adds the on-drive RAM caches together, so for example a RAID 0 C: drive, made from 2 RE4 drives each of which sports 64 MB on-drive cache) now delivers 2 x SATA 2 transfer rates with 128 MB on-drive cache.  This, along with enabling of Windows 7's highest throughput caching (which is not on by default) means that drive C: access will always be surprisingly quick.
FYI, I recently purchased a powerful dual quad core workstation that implements the above on the cheap...   I've described how in these threads.  Depending on your budget, possibly worth considering in lieu of a new build...
http://forums.adobe.com/message/3570020#3570020
http://forums.adobe.com/message/3605467#3605467
-Noel