This is intresting. I thought all Vertex 2 SSDs are good choices for ZIL
but this does not seem to be the case.
According to http://www.legitreviews.com/article/1208/1/ Vertex 2 LE,
Vertex 2 Pro and Vertex 2 EX are SF-1500 based but Vertex 2 (without any
suffix) is SF-1200 based.
Here is the table:
Model Controller Max Read Max Write IOPS
Vertex 2 SF-1200 270MB/s 260MB/s 9500
Vertex 2 LE SF-1500 270MB/s 250MB/s ?
Vertex 2 Pro SF-1500 280MB/s 270MB/s 19000
Vertex 2 EX SF-1500 280MB/s 270MB/s 25000
21.05.2010 17:09, Attila Mravik kirjoitti:
AFAIK OCZ Vertex 2 does not use volatile DRAM cache but non-volatile NAND
grid. Whether it respects or ignores the cache flush seems irrelevant.
There has been previous discussion about this:
http://comments.gmane.org/gmane.os.solaris.opensolaris.zfs/35702
"I'm pretty sure that all SandForce-based SSDs don't use DRAM as their
cache, but take a hunk of flash to use as scratch space instead. Which
means that they'll be OK for ZIL use."
Also:
http://www.techspot.com/news/37729-ocz-vertex-2-pro-100gb-ssd-review.html
"Another benefit of SandForce's architecture is that the SSD keeps
information on the NAND grid and removes the need for a separate cache
buffer DRAM module. The result is a faster transaction, albeit at the
expense of total storage capacity."
"So if I interpret them correctly, what they chose to do with the current
incarnation of the architecture is actually reserve some of the primary
memory capacity for I/O transaction management."
"In plain English, if the system gets interrupted either by power or by a
crash, when it initializes the next time, it can read from its transaction
space and "resume" where it left off. This makes it durable."
Here is a detailed explanation of the SandForce controllers:
http://www.anandtech.com/show/3661/understanding-sandforces-sf1200-sf1500-not-all-drives-are-equal
So the SF-1500 is enterprise class and relies on a supercap, the
SF-1200 is consumer class and does not rely on a supercap.
"The SF-1200 firmware on the other hand doesn’t assume the presence of
a large capacitor to keep the controller/NAND powered long enough to
complete all writes in the event of a power failure. As such it does
more frequent check pointing and doesn’t guarantee the write in
progress will complete before it’s acknowledged."
As I understand it, the SF-1200 will ack the sync write only after it
is written to flash thus reducing write performance.
There is an interesting part about firmwares and OCZ having an
exclusive firmware in the Vertex 2 series which based on the SF-1200
but its random write IOPS is not capped at 10K (while other vendors
and other SSDs from OCZ using the SF-1200 are capped, unless they sell
the drive with the RC firmware which is for OEM evaluation and not
production ready but does not contain the IOPS cap).
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