If you're gonna modernize that setup, I'll have to say that a cheap SSD for buffering will negate any future issues. Cheap PCIe SSDs are almost here (the cheap PCIe Sandforce controller chip was just released... consumer-ready PCIe SSDs ought to be around in just a couple of years).
The M.2 SSDs and PCIe SSDs are faster of course, which is why Consumer PCIe SSDs are getting pushed out by LSI and others. There isn't much point to faster SSDs when you're limited by the 6Gbps SATA port.
Modern NAND based SSDs wear out, their individual cells can be rewritten only so many time. So a big drive even with a smallish buffer is a consumable, although maybe the numbers work out now. They didn't ~3 years ago when I set up my current system.
The TLC SSD (3-bits per cell) is showing minor issues after 600TB of writing, but is still a usable drive. The MLC (2-bits per cell) SSDs have shown no issues after 600TB.
In comparison, a tape-drive would have long-past its ~200 end-to-end reads rating. MLC SSDs wear out slower than a tape drive! (Please don't take this sentence too seriously. I know I'm using hyperbole)
The SSDs I've linked to are MLC (2-bits per cell) designs, and can be expected to have roughly the same endurance as the MLC SSDs that techreport is testing.
By far the most telling takeaway thus far is the
fact that all the drives have endured 600TB of
writes without dying. That's an awful lot of
data—well over 300GB per day for five years—and
far more than typical PC users are ever likely to
write to their drives.
Besides, the backing storage is Tape. You're only using the SSD as a temporary stop so that your writes can be buffered out all at once. Using an SSD as a caching option has been extensively tested! Its safe to use for this sort of thing.
I think that's a bit past hyperbole, that's 200 end-to-end "wraps" per tape cartridge. A tape drive is (in theory) a LOT more durable, my drive has an official MTF of 250,000 hours at a 100% duty cycle.
That said, at least for my purposes, using one such SSD drive as a 5+ year "consumable" would work just fine, and the price for the Intel 335 is just fine.
(On the third hand, since all my system "disks" are LSI RAID 1 2 disk mirrors, I had all the infrastructure to add a 3rd drive, and I trusted Seagate enterprise SAS drives more than I trusted SSDs of that class 3 years ago (not that the latter were big and durable enough back then, unless perhaps you went to the $$$$$$ enterprise level of SSDs drives), I use the drive for some other backup systems, like sending my most important data to rsync.net using rsyncrypto, so I need some speedy disk to disk action. When I do a major system refresh in 2+ years I'll seriously consider SSDs, or if I have to replace my LTO-4 drive before then and need to seriously look at LTO-5 drives and media; I just passed the 2 LTO-4 tapes per monthly full backup threshold....)
Its possible to max out the 6GBps channel (ie: 480MB/s) with say... a $90 120GB Vertex-3. (http://www.amazon.com/OCZ-Vertex-2-5-Inch-Performance-VTX3-2...).
The M.2 SSDs and PCIe SSDs are faster of course, which is why Consumer PCIe SSDs are getting pushed out by LSI and others. There isn't much point to faster SSDs when you're limited by the 6Gbps SATA port.
For example: $300 for the 240GB Plextor M6e, with read speeds measured at ~667 MB/s: http://www.newegg.com/Product/Product.aspx?Item=N82E16820249...
So SSDs are actually both cheaper, and more performant than a 15k SAS buffering drive!