>>>>> "ms" == Michal Suchanek <hramrach%centrum.cz@localhost> writes: ms> Slow write performance tends to be the major factor behind ms> slow adoption of SSDs People on the ZFS list say the SSD's with SATA interface are always faster in io/s (like 10 - 50x faster) compared to single spindles of high-RPM SAS, and some of them are faster for streaming write throughput as well. ms> the datasheet says that the disk has dynamic wear leveling they all have this. no exceptions. FLASH cannot work without it. If it's SSD with SATA interface, the wear-leveling issue is fragmentation: http://www.pcper.com/article.php?aid=691 which silently degrades performance. Whether or not it happens depends on the quality of the closed-source wear leveling algorithm they use. I have this in my notes about SATA SSD: -----8<----- There's a problem in the MLC SSD drives with particular JMicron controller chips where some patterns of small writes trigger ~~10sec. hangs, which is most often called "stuttering" in online discussions of it that I've seen. My particular example is an OCZ Core 2 64GB unit. (David Dyer-Bennet) -----8<----- If the problem is real, it's likely not just OCZ. There were other rumors that Mtron and Imation are the same, and that all the Dell SSD's are Samsung. I don't know how many genuinely unique brands are actually in play right now. and MLC vs SLC used to be something about which people dragged out whiteboards and ranted for hours, but it is now a little silly because most drives marked MLC have a small SLC write cache in front, and sometimes also DRAM+supercap. It seems like it's really the proprietary control software that they're selling, not a commodity microchip plus board, so figuring out how many unique brands are in play is what needs doing now, not last year's MLC vs SLC. However, if by SSD you mean ``USB stick'', yes, writes are mind-blowingly slow. Some of them also have really crappy wear leveling and won't outlast a month if you are doing builds on them. Others do fine for much longer. The price of good sticks vs bad ones doesn't differ. Have a look to the reviews on newegg---that's the only way I've foudn to tell them apart. Then I just bought four different brands and waited to see which ones survived. Finally understand that NAND FLASH has a read-disturb property, so the wear leveling algorithm needs to keep track of how many times a cel is read, and rewrite it before it gets marginal---how much you want to bet USB sticks just skip this part? Anyway, of the ones that die within a month, some fail totally, meaning they don't even attach any more. Others are sneakier and fail by becoming read-only. I had one in a Linux box with as much RAM as the used space on the filesystem, and I didn't notice it had broken several days past until weird behavior made me look in dmesg, so even though the thing was ``clever'' enough to preserve my already-written data by failing to read only, the crappy exception handling of the overall storage stack meant that I still lost several days worth of writes that never made it to disk and never returned an error to userland. The storage failure handling of most OS's seems to really blow chunks.
Description: PGP signature