Re: [zfs-discuss] Sun Flash Accelerator F20
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 1/10th 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
Re: [zfs-discuss] Sun Flash Accelerator F20
I've already explained how you can scale up IOP #'s and unless that is your real workload, you won't see that in practice. See, running a high # of parallel jobs spread evenly across. I don't find the conversation genuine, so I'm not going to continue it. -Original Message- From: Richard Elling [mailto:richard.ell...@gmail.com] Sent: 2009-10-20 16:39 To: Dupuy, Robert Cc: zfs-discuss@opensolaris.org Subject: Re: [zfs-discuss] Sun Flash Accelerator F20 On Oct 20, 2009, at 1:58 PM, Robert Dupuy 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 ... but they don't say where it was measured or how big it was... http://www.sun.com/storage/disk_systems/sss/f5100/specs.xml Sun: F5100 read latency 410 microseconds ... for 1M transfers... I have no idea what the units are, though... bytes? http://www.fusionio.com/PDFs/Data_Sheet_ioDrive_2.pdf Fusion-IO: read latency less than 50 microseconds Fusion-IO lists theirs as .05ms ...at the same time they quote 119,790 IOPS @ 4KB. By my calculator, that is 8.3 microseconds per IOP, so clearly the latency itself doesn't have a direct impact on IOPs. I find the latency measures to be useful. Yes, but since we are seeing benchmarks showing 1.6 MIOPS (mega-IOPS :-) on a system which claims 410 microseconds of latency, it really isn't clear to me how to apply the numbers to capacity planning. To wit, there is some limit to the number of concurrent IOPS that can be processed per device, so do I need more devices, faster devices, or devices which can handle more concurrent IOPS? 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. cool. 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. Note: the F5100 has SAS expanders which add latency. -- richard (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. -- This message posted from opensolaris.org ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
Re: [zfs-discuss] Sun Flash Accelerator F20
This is one of the skimpiest specification sheets that I have ever seen for an enterprise product. At least it shows the latency. This is some kind of technology cult, I've wondered into. I won't respond further. -Original Message- From: Bob Friesenhahn [mailto:bfrie...@simple.dallas.tx.us] Sent: 2009-10-20 21:54 To: Richard Elling Cc: Dupuy, Robert; zfs-discuss@opensolaris.org Subject: Re: [zfs-discuss] Sun Flash Accelerator F20 On Tue, 20 Oct 2009, Richard Elling wrote: Intel: X-25E read latency 75 microseconds ... but they don't say where it was measured or how big it was... Probably measured using a logic analyzer and measuring the time from the last bit of the request going in, to the first bit of the response coming out. It is not clear if this latency is a minimum, maximum, median, or average. It is not clear if this latency is while the device is under some level of load, or if it is in a quiescent state. This is one of the skimpiest specification sheets that I have ever seen for an enterprise product. Sun: F5100 read latency 410 microseconds ... for 1M transfers... I have no idea what the units are, though... bytes? Sun's testing is likely done while attached to a system and done with some standard loading factor rather than while in a quiescent state. ...at the same time they quote 119,790 IOPS @ 4KB. By my calculator, that is 8.3 microseconds per IOP, so clearly the latency itself doesn't have a direct impact on IOPs. I would be interested to know how many IOPS an OS like Solaris is able to push through a single device interface. The normal driver stack is likely limited as to how many IOPS it can sustain for a given LUN since the driver stack is optimized for high latency devices like disk drives. If you are creating a driver stack, the design decisions you make when requests will be satisfied in about 12ms would be much different than if requests are satisfied in 50us. Limitations of existing software stacks are likely reasons why Sun is designing hardware with more device interfaces and more independent devices. Bob -- Bob Friesenhahn bfrie...@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/ GraphicsMagick Maintainer,http://www.GraphicsMagick.org/ ___ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
