I meet some strange low performance when run RAID0 with vanilla kernel
2.4.27/2.6.11.12.
My box is a 2.8G P4 and 1G RAM. 8 400GB SATA disk and A marvel 8port
controller. I run marvel 3.4.1 driver. I wrote a small program to write
device sequentially and SYNCHRONOUSLY.
This is performance of 1 disk. looks fine.
1048576Bytes * 1024 : 55.466MB/s
524288Bytes * 2048 : 55.830MB/s
262144Bytes * 4096 : 55.782MB/s
131072Bytes * 8192 : 55.567MB/s
65536Bytes * 16384 : 55.926MB/s
32768Bytes * 32768 : 54.344MB/s
16384Bytes * 65536 : 41.415MB/s
8192Bytes * 65536 : 26.499MB/s
4096Bytes * 65536 : 15.110MB/s
2048Bytes * 65536 : 8.422MB/s
1024Bytes * 65536 : 4.318MB/s
But when run 2 disk raid0, there is only 10% improvement.
md3 : active raid0 sdb[1] sda[0]
781422592 blocks 64k chunks
1048576Bytes * 1024 : 67.300MB/s
524288Bytes * 2048 : 66.796MB/s
262144Bytes * 4096 : 65.728MB/s
131072Bytes * 8192 : 65.017MB/s
65536Bytes * 16384 : 59.223MB/s
32768Bytes * 32768 : 49.766MB/s
16384Bytes * 65536 : 39.162MB/s
8192Bytes * 65536 : 26.386MB/s
4096Bytes * 65536 : 15.084MB/s
2048Bytes * 65536 : 8.383MB/s
1024Bytes * 65536 : 4.303MB/s
And when use 4 disks, the speed is slower!
md0 : active raid0 sdh[3] sdg[2] sdf[1] sde[0]
1562845184 blocks 64k chunks
1048576Bytes * 1024 : 58.032MB/s
524288Bytes * 2048 : 56.994MB/s
262144Bytes * 4096 : 58.289MB/s
131072Bytes * 8192 : 65.999MB/s
65536Bytes * 16384 : 59.723MB/s
32768Bytes * 32768 : 50.061MB/s
16384Bytes * 65536 : 38.689MB/s
8192Bytes * 65536 : 26.169MB/s
4096Bytes * 65536 : 15.169MB/s
2048Bytes * 65536 : 8.378MB/s
1024Bytes * 65536 : 4.287MB/s
Any hint on this?
* I do not know how to check current PCI bus speed and I am not sure
whether is limited by that. It is a 64bit card but I am not sure if it
is run at 66MHZ. Should be, but want to check to make sure.
* I tested each disk and all disk performs OK.
Thanks
Ming
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