On 11/06/2010 10:58, Andrey Kuzmin wrote:
On Fri, Jun 11, 2010 at 1:26 PM, Robert Milkowski <mi...@task.gda.pl <mailto:mi...@task.gda.pl>> wrote:On 11/06/2010 09:22, sensille wrote: Andrey Kuzmin wrote: On Fri, Jun 11, 2010 at 1:54 AM, Richard Elling <richard.ell...@gmail.com <mailto:richard.ell...@gmail.com><mailto:richard.ell...@gmail.com <mailto:richard.ell...@gmail.com>>> wrote: On Jun 10, 2010, at 1:24 PM, Arne Jansen wrote: > Andrey Kuzmin wrote: >> Well, I'm more accustomed to "sequential vs. random", but YMMW. >> As to 67000 512 byte writes (this sounds suspiciously close to 32Mb fitting into cache), did you have write-back enabled? > > It's a sustained number, so it shouldn't matter. That is only 34 MB/sec. The disk can do better for sequential writes. Note: in ZFS, such writes will be coalesced into 128KB chunks. So this is just 256 IOPS in the controller, not 64K. No, it's 67k ops, it was a completely ZFS-free test setup. iostat also confirmed the numbers. It's a really simple test everyone can do it. # dd if=/dev/zero of=/dev/rdsk/cXtYdZs0 bs=512 I did a test on my workstation a moment ago and got about 21k IOPS from my sata drive (iostat). The trick here of course is that this is sequentail write with no other workload going on and a drive should be able to nicely coalesce these IOs and do a sequential writes with large blocks.Exactly, though one might still wonder where the coalescing actually happens, in the respective OS layer or in the controller. Nonetheless, this is hardly a common use-case one would design h/w for.
in the above example it happens inside a disk drive. -- Robert Milkowski http://milek.blogspot.com
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