2009/9/10 Linux Raid Study <linuxraid.study@xxxxxxxxx>: > Hello: > > According to Wiki at http://linux-raid.osdl.org/index.php/Performance, > disabling NCQ helps in improving perf....I thought enabling > command-queuing helps is perf improvement. Can someone pls elaborate > how disabling NCQ helps.... > > I have 3 seagate HDDs (7200RPM) and 2 WD VelcoiRaptor (10k RPM) and > disabling NCQ doesn't help in performance.... > > thanks! First, you are familiar with what NCQ is, right? http://en.wikipedia.org/wiki/Native_Command_Queuing So, the linux kernel has extremely good elevator sorting algorithms of its own. So if the data is sent to the drive in the optimum order to reduce disk seeks, any additional sorting the disk does can result in unneeded overhead. So it comes down to the disks sorting characteristics. If they are top-end and thus better than the kernel does, then NCQ helps. If low-end and thus worse than the kernel does, then it hurts. Or so I understand it. Greg -- 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
