On 2011-08-03 22:33, Martin Steigerwald wrote: > Am Mittwoch, 3. August 2011 schrieb Jeff Moyer: >> Martin Steigerwald <Martin@xxxxxxxxxxxx> writes: >>> - ioengine=libaio >>> - direct=1 >>> - and then due to direct I/O alignment requirement: bsrange=2k-16k >>> >>> So I now also fully understand that ioengine=sync just refers to the >>> synchronous nature of the system calls used, not on whether the I/Os >>> are issued synchronously via sync=1 or by circumventing the page >>> cache via direct=1 >>> >>> Attached are results that bring down IOPS on read drastically! I >>> first let sequentiell.job write out the complete 2 gb with random >>> data and then ran the iops.job. >> >> If you want to measure the maximum iops, then you should consider >> driving iodepths > 1. Assuming you are testing a sata ssd, try using a >> depth of 64 (twice the NCQ depth). > > Yes, I thought about that too, but then also read about the > "recommendation" to use an iodepth of one in a post here: > > http://www.spinics.net/lists/fio/msg00502.html > > What will be used in regular workloads - say Linux desktop on an SSD here? > I would bet that Linux uses what it can get? What about server workloads > like mail processing on SAS disks or fileserver on SATA disks and such > like? > > > Twice of > > merkaba:~> hdparm -I /dev/sda | grep -i queue > Queue depth: 32 > * Native Command Queueing (NCQ) > > ? > > Why twice? Twice is a good rule of thumb, since it allows both the drive some freedom for scheduling to reduce rotational latencies, but it also allows the OS to work on a larger range of requests. This is beneficial mostly for merging of sequential requests, but also for scheduling purposes. So at least depth + a_few, 2*depth is a good default. -- Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe fio" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
