Messages in this thread | | | From | "" <> | Date | Thu, 20 Dec 2001 12:22:33 -0000 | Subject | raw devices |
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I have been performing some tests on raw devices, the results of which I do not understand. I have 4 FC busses, each with one SCSI disk, connect to a Linux system running 2.4.16. I use the raw command to bind /dev/raw1 - /dev/raw4 to each of the devices. With one process per raw device, running large sequential reads, I got a total throughput of 340 Megabytes per second. I also observed 85% CPU idle. Following this I performed some more tests and then returned to this one. This time the total had gone down to 180 and there was no free CPU. I realized that the first time I ran the tests, each of the disks that the raw devices were mapped to were mounted. I then verified that this data was being transferred along the FC bus using an analyzer while the devices were mounted. Can anyone explain this to me ? I find it hard to believe that the disk should be permitted to be mounted when using raw device mappings. If the disks should not be mounted why is there such a great performance difference ?
Many Thanks
Simon. __________________________
Simon Haynes - Baydel Phone : 44 (0) 1372 378811 Email : simon@baydel.com __________________________ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.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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