My take on the responses I've received the last days, is that it isn't genuine.
________________________________ From: Tim Cook [mailto:t...@cook.ms] Sent: 2009-10-20 20:57 To: Dupuy, Robert Cc: zfs-discuss@opensolaris.org Subject: Re: [zfs-discuss] Sun Flash Accelerator F20 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-pro duct-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
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