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Message-ID: <da824cf30810131833g6e509d0dvb6cce6c7220a1a28@mail.gmail.com> Date: Mon, 13 Oct 2008 18:33:55 -0700 From: "Grant Grundler" <grundler@...gle.com> To: "kenneth johansson" <ken@...jo.org> Cc: linux-ide@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: weird throughput on write to SATA disk On Mon, Oct 13, 2008 at 3:19 PM, kenneth johansson <ken@...jo.org> 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-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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