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Linux Storage and Filesystem Workshop, day 2

Apr 28, 2009, 20:02 (0 Talkback[s])
(Other stories by Jonathan Corbet)

"Matthew Wilcox, who led the discussion, started by noting that Intel SSDs are able to handle a large number of operations in parallel. The parallelism is so good, in fact, that there is really little or no advantage in delaying operations. I/O requests should be submitted immediately; the block I/O subsystem shouldn't even attempt to merge adjacent requests. This message was diluted a bit later on, but the core message is clear: the kernel should, when driving an SSD, focus on getting out of the way and processing operations as quickly as possible.

"It was asked: how do these drives work internally? This would be nice to know; the better informed the kernel developers are, the better they can do at driving the devices better. It seems, though, that the firmware in these devices - the part that, for now, makes Intel devices work better than most of the alternatives - is laden with Valuable Intellectual Property, and not much information will be forthcoming. Solid-state devices will be black boxes for the foreseeable future.

"In any case, current-generation Intel SSDs are not the only type of device that the kernel will have to work with. Drives will differ greatly in the coming years. What the kernel really needs to know is a few basic parameters: what kind of request alignment works best, what request sizes are fastest, etc. It would be nice if the drives could export this information to the operating system. There is a mechanism by which this can be done, but current drives are not making much information available."

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