Solid-state storage devices and the block layer

Posted Oct 15, 2010 17:42 UTC (Fri) by jmy3056 (guest, #70648)
Parent article: Solid-state storage devices and the block layer

I think the analogy presented misses the mark. Instead of equating block IO with Network improvements consider this.

Media that stores electronic information that used to spin but now doesn't is a closer parallel with RAM. Optimzations for "disk" IO need to follow a similar path as OS/kernels when dealing with RAM.

Solid-state storage devices and the block layer

Posted Oct 22, 2010 22:04 UTC (Fri) by eds (guest, #69511) [Link]

There are many good reasons to treat NAND flash storage more like disk than like DRAM.

1. Addressing: DRAM is byte/word addressable; NAND flash is not. NAND flash pages are currently 4KB in size and must be read/written
2. Flash management: flash sucks. It has long erase times, needs wear-leveling, needs lots of ECC and redundancy to be reliable. Dealing with flash requires a lot of careful management that nobody's going to want on a DRAM-like path.
3. Speed: flash is a lot faster than disk. But it's still a lot slower than DRAM (a write to a busy NAND part may have to wait up to 1ms).
4. Size: it's very expensive to try to address a terabyte of DRAM. 64-bit CPUs don't actually implement a full 64-bit address space. It's much cheaper to just address huge storage devices in blocks, like a disk.

If in a few more years phase-change memory becomes big and cheap enough to give NAND flash a run for its money, then it may be time to start treating nonvolatile memory sort of like DRAM. But that day isn't quite here yet.