Saturday, 6 June 2009

RAID0 + SSD = speed!

I've been messing around with Ubuntu Jaunty Desktop installed on two SanDisk 32GB pSSD devices today with a RAID0 configuration and I'm really impressed with the performance. (Thanks to SanDisk for providing me with some early samples to test!)

RAID0 stripes data across the two SSDs which should theoretically double I/O rates. It also allows me to effectively create a larger disk volume by treating both drives as one larger combined device. The downside is that if one SSD fails, I have zero redundancy (unlike RAID1) and hence can lose my data.

To avoid controller saturation, I configured the SSDs so that each SSD used a different SATA controller; I believe this helps, but I've not done any serious benchmarking to verify this configuration assumption.

I used the SoftwareRAID wiki page as a quick start guide to get my head around how to configure my system; I created a small /boot partition and then a 30GB and ~2GB RAID0 volumes for / (using ext4) and swap respectively on each drive and then installed the 64 bit Jaunty Desktop using the alternative installer ISO image.

Performance just rocked! I benchmarked block I/O performance using bonnie and got block write rates of ~73MB/s and reads of ~114MB/s.

A quick test with dd writing 8GB of zeros in 4K blocks on my machine hit ~102MB/s write rate - quite astounding. I managed to get a sustained read rate of ~119MB/s read rate in 4K blocks reading a 16GB file - that's just awesome!

Boot time was impressive too. On my dual core 2.0GHz desktop I booted in ~12-14 seconds after grub stage without any optimization tweaks.

If I get some more spare time I will try and figure out how to get the partitions aligned to 128K block boundary to see how much more performance I can squeeze out of these SSDs. Watch this space!

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