On Sun, Jun 24, 2007 at 12:59:10PM -0400, Justin Piszcz wrote: > Concerning NCQ/no NCQ, without NCQ I get an additional 15-50MB/s in speed > per various bonnie++ tests. There is more going on than a bad NCQ implementation of the drive imho. I did a long test over night (and still only got two schedulers done, will do the other two tomorrow), and the difference between a queue depth of 1 and 2 is DRAMATIC. See http://www.xs4all.nl/~carlo17/noop_queue_depth.png and http://www.xs4all.nl/~carlo17/anticipatory_queue_depth.png The bonnie++ tests are done in a directory on the /dev/md7 and /dev/ssd2 partitions respectively. Each bonnie test is performed four times. The hdparm -t tests (that show no difference with a -tT test) are each done five times, for /dev/sdd, /dev/md7 and /dev/sda (that is one of the RAID5 drives used for /dev/md7). Thus in total there are 2 * 4 + 3 * 5 = 23 data points per queue depth value in each graph. The following can be observed: 1) There is hardly any difference between the two schedulers (noop is a little faster for the bonny test). 2) An NCQ depth of 1 is WAY faster on RAID5 (bonnie; around 125 MB/s), the NCQ depth of 2 is by far the slowest for the RAID5 (bonnie; around 40 MB/s). NCQ depths of 3 and higher show no difference, but are also slow (bonnie; around 75 MB/s). 3) There is no significant influence of the NCQ depth for non-RAID, either the /dev/sda (hdparm -t) or /dev/sdd disk (hdparm -t and bonnie). 4) With a NCQ depth > 1, the hdparm -t measurement of /dev/md7 is VERY unstable. Sometimes it gives the maximum (around 150 MB/s), and sometimes as low as 30 MB/s, seemingly independent of the NCQ depth. Note that those measurement were done on an otherwise unloaded machine in single user mode; and the measurements were all done one after an other. The strong fluctuation of the hdparm results for the RAID device (while the underlaying devices do not show this behaviour) are unexplainable. >From the above I conclude that something must be wrong with the software RAID implementation - and not just with the harddisks, imho. At least, that's what it looks like to me. I am not an expert though ;) -- Carlo Wood <carlo@xxxxxxxxxx> PS RAID5 (md7 = sda7 + sdb7 + sdc7): Three times a Western Digital Raptor 10k rpm (WDC WD740ADFD-00NLR1). non-RAID (sdd2): Seagate barracuda 7200 rpm (ST3320620AS). The reason that now I measure around 145 MB/s instead of 165 MB/s as reported in previous post (with hdparm -t /dev/md7) is because before I use hdparm -t /dev/md2, which is closer to the outside of the disk and therefore faster. /dev/md2 still is around 165 MB/s. - To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
