On Tue, Oct 20, 2009 at 3:58 PM, Robert Dupuy <rdu...@umpublishing.org>wrote:
> "there is no consistent latency measurement in the industry" > > You bring up an important point, as did another poster earlier in the > thread, and certainly its an issue that needs to be addressed. > > "I'd be surprised if anyone could answer such a question while > simultaneously being credible." > > > http://download.intel.com/design/flash/nand/extreme/extreme-sata-ssd-product-brief.pdf > > Intel: X-25E read latency 75 microseconds > > http://www.sun.com/storage/disk_systems/sss/f5100/specs.xml > > Sun: F5100 read latency 410 microseconds > > http://www.fusionio.com/PDFs/Data_Sheet_ioDrive_2.pdf > > Fusion-IO: read latency less than 50 microseconds > > Fusion-IO lists theirs as .05ms > > > I find the latency measures to be useful. > > I know it isn't perfect, and I agree benchmarks can be deceiving, heck I > criticized one vendors benchmarks in this thread already :) > > But, I did find, that for me, I just take a very simple, single thread, > read as fast you can approach, and get the # of random access per second, as > one type of measurement, that gives you some data, on the raw access ability > of the drive. > > No doubt in some cases, you want to test multithreaded IO too, but my > application is very latency sensitive, so this initial test was telling. > > As I got into the actual performance of my app, the lower latency drives, > performed better than the higher latency drives...all of this was on SSD. > > (I did not test the F5100 personally, I'm talking about the SSD drives that > I did test). > > So, yes, SSD and HDD are different, but latency is still important. > Timeout, rewind, etc. What workload do you have that 410microsecond latency is detrimental? More to the point, what workload do you have that you'd rather have 5microsecond latency with 1/100000th the IOPS? Whatever it is, I've never run across such a workload in the real world. It sounds like you're comparing paper numbers for the sake of comparison, rather than to solve a real-world problem... BTW, latency does not give you "# of random access per second". 5microsecond latency for one access != # of random access per second, sorry. --Tim
_______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
