On 9/19/2011 3:33 AM, Luke S. Crawford wrote:
The reason I said L2ARC and not ZIL for MLC consumer SSDs has to do
with size, performance, and price.
The maximum size for the ZIL is about 1/2 RAM, effective size is even
smaller, it needs enough to store about 10 seconds worth of writes. It
also needs to have very fast writes. Something like the STEC ZeusRAM
(a flash-backed RAM drive) or a small SLC SSD would be ideal.
Interesting product; probably out of my price range, though. It used
to be they would sell products that took normal DIMMS, battery back them,
and would output a normal sata connector. The last time I saw such a
device it only supported non-ecc ddr2, and thus was completely useless
to me.
I'll point out again, that if you just want to put ZIL on fast devices
to, say, make NFS accesses for small files and meta-data fast, the Intel
320 Series SSD is a good choice. In our benchmarks, it is as fast as the
older, more expensive X-25E SLC drive, plus it has the capacitor on
board to guarantee data integrity in power failure. I doubt you'd see
more than incremental improvements with the STEC at a very steep price
premium.
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