On 12/22/2012 11:29 PM, Roy Sigurd Karlsbakk wrote: >>> I have an array with 6 2TB drives plus a spare. While this works >>> well, I can from the munin graphs at >>> http://munin.karlsbakk.net/munin/karlsbakk.net/smilla.karlsbakk.net/index.html >>> that the WD2001FASS drives (sd[bcfg]) perform some 30% better than >>> the Hitachi HDS723020BLA642 drives (sd[eh]). The drives are on a >>> mixed set of controllers, so this shouldn't be relevant. Since they >>> all are specified to spin on 7200RPM, I find it wierd that the >>> performance difference shown by the Munin graph is so big. >> >> You've provided zero information about the controllers or the >> configuration of the drives. If the SATA ASIC to which the Black >> drives >> are connected is AHCI and the other is not, then NCQ may account for >> the >> difference in performance. Or, both may currently be AHCI, but >> possibly >> the Hitachi drives perform better with NCQ disabled. This would not be >> rare. If you laid partitions on the Hitachi drives and misaligned >> them, >> this could easily cause a 30% deficit. Etc, etc. >> >> I doubt there is a 30% overall performance difference between these >> two >> drive models. The Black models are "enthusiast" class drives, and do >> have some additional performance features, but not that I'd think >> would >> yield a 30% advantage. >> >> You need to dig deeper into the details. > > no partitions on this setup, just plain drives. what munin tells me is those WD drives are rather faster than the hitachis. As noted, all drives are on a mixed controller setup, the hitachis and wd drives share controllers for some. the only known common factor for the slow and fast drives are their label. I just looked at your Munin graphs more closely. Your interpretation of 30% difference in performance doesn't seem to be accurate. All 6 drives have nearly identical daily and weekly avg IOs and throughput. The avg latency of the Hitachi drives is a few milliseconds higher, but this doesn't seem to be negatively affecting IOPS or throughput. How are you determining your claimed 30% performance deficit? I don't see it. -- Stan -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
