New LSI 9200 series controllers: 6Gb/s, 2.88 GB/s seq. reads, 1.87 GB/s seq. writes

[Mastakilla]

With RAID-5, there's an additional benefit of write through caching, which is that the controller can buffer enough data to write full stripes at a time. The alternative is partial stripes, which require reading-then-writing the parity disk. With a full-stripe write, the parity drive is just written, and not read first. With rotating media, there is a huge performance difference, since you don't have to wait for the drive to make a full rotation before writing.

I suppose you mean write back instead of write through?