SATA RAID3 SLOW!

[nats1956]

I temp running my OS on a 250gb 16mb Seagate PATA with a Raid3 array of 5 HD's( 3-Maxtor 320gb 16mb and 2-WD 320gb 8mb). When I run HD Tach I only get about 59-60mb average read random access of 22.2ms on the ARRAY! What could be wrong? On the PATA I get about 59mb/s random access 15.8ms. Should I swap out the WD drives in the array and replace with Maxtor 320gb 16mb? I have 2 Maxtor coming back from RMA and would use those and then use the WD drive has my OS boot disk!

[Grentz]

You need to read up on RAID 3 then...

Random Read Performance: Good, but not great, due to byte-level striping.

Random Write Performance: Poor, due to byte-level striping, parity calculation overhead, and the bottleneck of the dedicated parity drive.

Sequential Read Performance: Very good.

Sequential Write Performance: Fair to good.


RAID 3 is good for Sequential Reads/Writes but not for Random...the test you ran is for random so it does not perform that well.

http://www.pcguide.com/ref/hdd/perf/raid/levels/singleLevel3-c.html

[draksia]

You need to read up on RAID 3 then...

Random Read Performance: Good, but not great, due to byte-level striping.

Random Write Performance: Poor, due to byte-level striping, parity calculation overhead, and the bottleneck of the dedicated parity drive.

Sequential Read Performance: Very good.

Sequential Write Performance: Fair to good.


RAID 3 is good for Sequential Reads/Writes but not for Random...the test you ran is for random so it does not perform that well.

http://www.pcguide.com/ref/hdd/perf/raid/levels/singleLevel3-c.html

It is extremely unlikely that his raid card is doing raid 3 which is byte level striping. Most things that claim to using raid 3 are really doing raid 4 which is the same thing but at a chunk level usually 64k.

While on a good powerful raid card raid 5 might be a little faster on most consumer level products would never even see a difference.

[Grentz]

Still, it could explain his problem of bad random access times/speeds :)