[email protected] wrote: >> >> >> 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) > > although unless the drive includes battery backup for the DRAM you > will loose a lot of data if the drive looses power. oops. Typo on my part. super 'capacitor', which acts as a battery in that it flushes the DRAM to nonvolatile flash storage
>> 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) > > are you comparing this to having the ZFS intent log on the same drives > as your other data? or are you comparing it to having your ZFS intent > log on a dedicated high-speed rotating drive? > zfs normally stripes the intent log across the data disks unless you tell it otherwise (e.g. 46 disks on a Sun x45000 or x4540) You can also put the ZIL on a dedicated high speed rotating drive. The x25E outperforms both except in the case where you want high sequential throughput. >> 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. > > the Fusion IO card is fast, but it's also extrememly expensive. > aye.. I did mention that in the second sentence.. >> 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. > > if you really need fast writes you need battery backed ram. if you > don't need very much (up to a couple of gigs with the writes being > converted from many small writes to a few large writes by the > hardware) you can use a raid card/chassis with it. if you need a lot > you can look at something like ACard's ANS-9010 Serial ATA RAM disk ( > http://techreport.com/articles.x/16255 ), it's as much faster than a > X25E as an X25E is from a normal hard drive. > I have evaluated a battery backed ram that was much slower than flash for ZIL purposes. I will spare the vendor some embarassment, but I was very surprised with the results and still don't fully understand why. _______________________________________________ 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/
