30 MB/s RAID5 write speed on Nforce 790i. Something wrong?

[fzkl]

I have 3 X 1.5 TB HDDs on an nForce 790i SLI motherboard in a RAID5 configuration. My write speeds to this drive is around 30 MB/s which seems tragically low. Is something wrong or is this the best I can expect because of the software RAID implementation?

Thanks in advance.

 

[Emulex]

hi welcome to pseudo-software raid. it is tragically LAME.

raid-5 and raid-6 require a write read write - your lack of cache helps immensely at slowing things down.

plunk down for a nice raid card with BBWC and maybe you'll get triple that!

lol.

 

[bigi]

Yea, RAID5 needs true and good hardware for calculations. Even with this, it is not write speed champion in certain applications.

 

[Mark R]

It's not so much that RAID 5 needs a hardware RAID card - rather it just needs decent software.

Of course, with a hardware RAID card, the card will have some highly optimised firmware installed on it's CPU.

For example, a core i7 CPU running a modern good quality software RAID 5 or 6 system (e.g. as found in linux) can out-perform high-end RAID cards on the same system by a worthwhile margin (10-20% extra sequential throughput and 10-15% extra IOPS) at the cost of modest CPU (1 core of an i7 is good for about 1GB /s write throughput) and RAM usage.

The problem is that motherboard 'fakeraid' isn't optimised - it's basically, barely good enough to work.

A big problem with RAID 5 is that small writes (smaller than 1 complete stripe) must be translated into write - read - write. However, this shouldn't be a problem for large sequential writes (if the write fills an entire stripe, then there is no need to read the strip to modify it, you just overwrite the whole stripe) - however, I can easily see uber lame RAID drivers reading the stripe before overwriting it.