Ubuntu Installation :: Unacceptable Write Performance Of Software Raid1 On Lucid Server?

Compared to my laptop notebook with a HD of 5400rpm, the write performance of raid1 on an ubuntu lucid server is unacceptable. In the begining, I installed ubuntu 9.04 server(alternate) using raid1 with two WD 1TB HDs of 7200rpm(Green Power) and then performed dist upgrade to 9.10 and then to 10.04.

I guess the write performance initially was reasonable since the installation and data migration(copy from another computer over LAN) didn't take too much time. However, after upgrading the server to 9.10 or so, I found large file upload through samba or ftp tends to block and time out. It is of no use whether to change the daemon or the client program so that I tried to test the read/write performance on the server to figure out the situation.

To my surprise, using strace I found even a simple program like cp would easily get blocked eventually in a write() system call for decades of seconds. Hence, I perform another disk writing test using dd for data size ranging from 50MB to 1GB. Performance test commands are listed as follows:

Quote: dd if=/dev/zero of=test.img count=[5|10|15|20|100] bs=10M

if the data to write is equal or fewer than 150MB, the command returns immediately at very hight speed but the raid disks starts to sync and busy so that the terminal prompt seems to freeze. I think this behavior is normal under the raid1 configuration, isn't it?

But when the data size is equal to 200MB, the test command blocks for seconds and the write speed is measured at about 16.6MB/s. Of course, the raid disk still starts to sync and busy afterwards. Next, I test writing with data of size 1GB. The command blocks so long for about 770 seconds(<2MB/s) while the same test runs for only 17.49 seconds(60MB/s) on my laptop.

I also burn a Lucid LiveCD to boot the server and mount the raid device to run the test again but the results remain similar. Does that means even I re-install the system on the raid, the problem never disappears?

PS: the disks run under the mode of UDMA6 without change.