Saturday, June 19, 2010

Painfully slow raid CentOS system

SkyHi @ Saturday, June 19, 2010

Today I was installing CentOS 5.2 to a Tyan barebone server with Intel Xeon X3220 processor, 2GB of RAM, and 2 Western Digital SATA II 250GB HDD. I chose to use software RAID 1 for my /boot and /. I didn’t create RAID 1 for swap partition because it is useless and in fact it might slow down performance. It took more than 2 hours to complete the whole installation process even when I used bare minimum packages selection. The format process of / partition itself took quite a while to complete.

Once the installation was complete, it rebooted and I found a painfully slow newly-installed CentOS system. The keyboard response was slow as if I were connected to a remote server with 1 second latency. I wasn’t happy because this is a quad-core processor server with acceptable amount of RAM. When I looked at /proc/mdstat to see how the software RAID is doing, I noticed that the sync speed is only around 1000KB/s. I tried looking for solutions on Google and found this and this. The solution I got didn’t help increase the sync speed, nor the slow response I was getting typing on the console or remotely.

I then somehow managed to find another possible solution. I can’t remember how I finally got this solution (thanks to nixCraft/CyberCiti). I didn’t notice that the hard drives were actually detected as hdX (IDE/PATA) instead of sdX (SATA). Now this makes sense because PATA is much slower than SATA. It turned out to be an issue with the hardware detection process. Somehow CentOS detected the HDDs and used PATA driver instead of SATA driver, so the devices were named hdX and treated as PATA hence the slow sync speed. I made the BIOS changes as mentioned in the solution and attempted another install, it was REALLY fast this time and the software RAID 1 sync speed was over 70000KB/s.