David Thanks for the response.. > 278MB/s read bandwidth to a locally attached samsung 840 pro on 1M > sequential reads is very low unless you have it accidentally plugged > into a SATA 3Gb/s port instead of a 6Gb/s. I'd sort out why you're not > seeing 500 MB+ on this as starting point for your investigation. I thought this was a good catch..so I tried hdparm -I /dev/sdb|egrep -i "Model|speed" and I get the same on both machines.. [root@lab-sj1-141 uc]# hdparm -I /dev/sdb|egrep -i "Model|speed" Model Number: Samsung SSD 840 PRO Series * Gen1 signaling speed (1.5Gb/s) * Gen2 signaling speed (3.0Gb/s) [root@lab-sj1-141 uc]# Does this imply they are running @3.0Gb/s with a peak rate of 300MB/s? I am using Dell Precision workstation T3600 and according to the specs it has 6G SAS ports which is where these drives are connected. I am not sure if this needs to be enabled some way. I rebooted and went through BIOS setting and did not see anything in the drives/storage sections. I ran the test on both machines and both got ~279MB/s for sequential reads. This does not explain why fio gives a higher number when one of the drives is exported over the network?! > Also, Sequential performance probably isn't what you want to look at for > a long latency block device (as opposed to without the network in the > way) as io merging could become the dominant factor for performance even > when using large block sizes to start. Your point noted. I ran all combinations of tests (read,write,readwrite,randread,randwrite,randrw) and did so with 1M and 512. I was looking for some consistency and trying to quantify the effect of latency on performance. > your latency data from the runs looks funny too - with the NBD latency > being lower than the locally attached on writes, but not for reads. > that would seem to indicate there is some buffering going on in the > system that you're not aware of that is making your results noisy (and > confusing) I agree that the latency number is confusing. I am trying to understand how fio is measuring the latency for a NBD and maybe that will help sort this out. thx, Kishore -- 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
