On Mon, Oct 13, 2008 at 3:19 PM, kenneth johansson <ken@xxxxxxxxx> wrote: ... >> Can you try "dd oflag=direct if=/dev/null of=/dev/sdb bs=64k"? > > I changed to use O_DIRECT and it's much more consistent now. 69-75 with > 74 about 95% of the time. That's low but it could be worse. Many things can contribute to slow disks. Favorites are overtemp (See SMART field 194) and vibration (no measurement possible w/o special equipment). "dd" isn't exactly a performance application until one uses really big block sizes (1MB or larger). sgp_dd is better since it is multi-threaded. fio has all the right knobs to test disk perf and measure it properly. > the disk is supposed to have 105 115 sustained > data rate. Where did 105-115 number come from? The best I've seen to date with 7200 rpm drives was 108MB/s on the outside diameter. That degrades slowly until about 60-70% towards the inside diameter and then drops off dramatically (down to something like 50MB/s). hth, grant -- 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
