Dave Close wrote: > Doug Hughes wrote: > > > > Flash reads are reasonably fast, I agree. Writes are not in my > experience. And one probably writes to swap at least as often as > one reads from it. > You should check out the Intel X-25E. There are 2 more commonly used flash technologies these days. There is the multi-level cell which has higher density but is slower on write and the single-level cell (SLC) which is faster on write (well under a millisecond) and lower on density. the MLC (e.g. X-25M) is typically used in cameras and consumer electronics. The SLC are more typically used on enterprise flash SATA or SAS interface drives.
There is also a number of newer devices that combine the advantages of 3 different technologies. The NAND flash, the NOR flash, and RAM all in one chip. the RAM is used as a buffer to accumulate writes and to satisfy reads from cache, NAND: small cell size, low cost per bit. High density. Poor random access. Fast bulk writes and reads by block programming. Fast writes, slow reads. fast erase. NOR: fast reads (100MB/s), slow writes, lower density, good random access. slow erase adding standard DRAM onto this with a super capacity for flushing the ram to nonvolatile flash gives you the best of all worlds. Its still relatively new and relatively expensive. I know of only one vendor using this in mainstream, and that's Sun with their Readzilla and Logzilla accelerators for FishWorks. (Other vendors may be doing similar, but I'm not aware of them) Most off the shelf flash drives are a combination of NOR and NAND chips to balance density with speed. As I mentioned earlier, using Flash for the ZFS intent log GREATLY speeds up zfs with NFS over spinning disk media, even when striped. You do pay some penalty in serial write bandwidth however. You become bottlenecked on the aggregate write throughput of the flash devices. On the other hand, if you're just pumping out TB of sequential data, there's no reason to even consider flash in the mix. Spinning media kicks butt in this arena (even tape does very well) The Fusion IO card is the fastest thing out there at the moment. It's part flash, part DRAM, like the logzilla but comes in a PCI-E form factor that you have to plug into a machine, and it's also very spendy, but if you really want to speed up your DB by orders of magnitude, you could shove some of these into a machine with a bunch of PCIE2 slots and mirror them together and throw indexes or small tables on here. So, I guess to summarize, before saying that flash writes aren't fast, have a test drive of the X-25E. Flash got a deservedly bad wrap in the past for write speed, but things have come a long way in the last couple of years. (note: I still wouldn't use flash for swap space, yet, but once TB flash is out, wear leveling and 1000000 cycle flash will make even that point moot) refs: http://www.google.com/url?sa=t&source=web&ct=res&cd=2&url=http%3A%2F%2Fwww.toshiba.com%2Ftaec%2Fcomponents%2FGeneric%2FMemory_Resources%2FNANDvsNOR.pdf&ei=MuerStjmCtHglAfYquW7Bg&rct=j&q=NOR+flash+vs+NAND+flash&usg=AFQjCNG04XmXaryk4ybCb5PsP3BwJOxKxw http://www.google.com/url?sa=t&source=web&ct=res&cd=3&url=http%3A%2F%2Fforums.techarena.in%2Fweb-news-trends%2F1090657.htm&ei=ZumrSpLtCsbllAfU2dTHBg&rct=j&q=sun+flash+1000000+write+cycles&usg=AFQjCNHxxyYuzcAQKtZNhb6fI7vhEj-9Ug pay particular attention to these two from SC08 conference http://www.pdsi-scidac.org/events/PDSW08/resources/papers/simsa_PDSW.pdf http://www.pdsi-scidac.org/events/PDSW08/resources/slides/simsa_PDSW.pdf _______________________________________________ Discuss mailing list [email protected] http://lopsa.org/cgi-bin/mailman/listinfo/discuss This list provided by the League of Professional System Administrators http://lopsa.org/
