> 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). _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
