SOLVED: Linux software RAID 5 too slow

In this article I am going to tell about my experience with Linux software RAID.
So I had a ASUS P6T motherboard which has Intel ICH10R raid controller, 3x 1 Tb SATA 2 HDDs and Intel Core i7 920 processor. So I wanted to install Fedora 10 on that machine.
After configuring RAID 5 in the BIOS I booted the Fedora 10 installation DVD to start the installation. BUT! Suddenly I saw that Anaconda see 3 separate hard drives instead of 1 RAID device. After some googleing I figured out that my motherboard don’t have real RAID controller. Instead it is fakeraid controller. It is just software raid which software is located in BIOS. So I decided to use linux software raid, because it is definitely better than the from ASUS.
So installed Fedora 10 with linux software RAID 5 with LUKS encryption. After installation machine started to work very slowly. I thought it so because of the encryption, but after some googleing I understood that the encryption can’t slow down the machine that way. The thing was when you newly create RAID 5 array it needs to build the 3rd hard drive and it take a lot of time. It took from me approximately 4 hours to finish that operation on 1 Tb hard drives. You can check the rebuild status at any time invoking one of the following commands:

# cat /proc/mdstat


# mdadm --detail /dev/md0

After rebuild was over and after some tunings (see tuning parameters below) I had ~90 Mb/s write and ~200 Mb/s read.

My tuning parameters was:

echo 32768 > /sys/block/md0/md/stripe_cache_size
blockdev --setra 65536 /dev/md0


  1. Thank you! The stripe_cache_size made my raid5 recovery go from 32Mb/s to 140Mb/s 😀


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