On Thu, Dec 11, 2008 at 12:12:37AM +0200, Raz Ben-Yehuda wrote: > I did not want to dive into details because it does not matter. Whether > noop,deadline, deadline parameters... > As for the controller I used 4 different controllers. Adaptec,AHCI and > Intel as Integrated chips on the 1025W-UR supermicro motherboard, and a > 4-th controller SuperMicro UIO Adaptec aac card. > All gave same results for most dd writes commands. > dd if=/dev/zero of=/dev/sda bs=1M count=1000 oflag=direct , and many > other variants such erase block size ( 128K ) , several erase block size > and so on. Kernel is 2.6.18-8.el5. OK, I suspect you aren't giving the drive enough work to do for it to perform at its best. Try doing something like this: for i in $(seq 0 9); do \ dd if=/dev/zero of=/dev/sda bs=1M count=1000 oflag=direct \ seek=$(($i * 1000)) & \ done > I used all on a supermicro 1025W-UR. Disks have a SAS interface, 80GB. > Also, I would like to note, I have 8 disks in array, while each one > perform READS 250 MB/s, together I degrade to 200 MB/s each. As for That doesn't surprise me; you're probably hitting a limitation either of the array or the cable itself. A SAS cable can run up to 6Gbps, which will be around 600MB/s. So three drives should be able to saturate your SAS cable. If you're using an x4 link, that goes up to 2400MB/s which should be ample for 8 drives ... maybe you're using a 3Gbps cable which would limit each drive to 150MB/s. -- Matthew Wilcox Intel Open Source Technology Centre "Bill, look, we understand that you're interested in selling us this operating system, but compare it to ours. We can't possibly take such a retrograde step." -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
