Only ~85MiB/s (e1000e/write) to ~310MiB/s RAID-0 on ATOM board?

[Justin Piszcz]

Hi,

Motherboard: Supermicro X7SPA-HF (MINI-ITX)

I tried changing various settings with ethtool, ifconfig, and e1000e 
module parameters.

=> I get ~310MiB/s write with 5 Raptor 150s in RAID-0
atom166:/r1# dd if=/dev/zero of=bigfile bs=1M count=10240
10240+0 records in
10240+0 records out
10737418240 bytes (11 GB) copied, 34.7194 s, 309 MB/s
atom166:/r1#


=> I get 239MiB/s read with 5 Raptor 150s in RAID-0
# dd if=bigfile of=/dev/null bs=1M count=10240
10240+0 records in
10240+0 records out
10737418240 bytes (11 GB) copied, 44.9199 s, 239 MB/s

When I use samba to push files to this RAID I only get between 80-90MiB/s 
instead of the usual 100-120MiB/s I see between my main (ATX) boards..  It 
seems to hover around 85MiB/s average..

I also tried an external PCI-e 1.0 Intel NIC, made no difference.  From 
the NM10 chipset block diagram, there should be enough bandwidth to fully 
saturate a gigabit link, is the CPU (Dual core Atom D510) too slow to 
achieve the maximum speed?

FTP is slightly faster:
`20101030-t500.tib' at 400541736 (3%) 88.72M/s eta:2m [Receiving data]
`20101030-t500.tib' at 565772280 (4%) 91.51M/s eta:2m [Receiving data]
`20101030-t500.tib' at 982224624 (7%) 94.75M/s eta:2m [Receiving data]
`20101030-t500.tib' at 1967568384 (15%) 96.39M/s eta:2m [Receiving data]
`20101030-t500.tib' at 2299966640 (17%) 96.90M/s eta:2m [Receiving data]

Getting the same file to an ATX motherboard:
`20101030-t500.tib' at 1020865896 (7%) 106.13M/s eta:2m [Receiving data] 
`20101030-t500.tib' at 1394552704 (10%) 107.53M/s eta:2m [Receiving data] 
`20101030-t500.tib' at 1861689088 (14%) 108.49M/s eta:97s [Receiving data] 
`20101030-t500.tib' at 2702497824 (21%) 109.56M/s eta:88s [Receiving data] 
`20101030-t500.tib' at 3636710872 (28%) 110.27M/s eta:80s [Receiving data]

Why cannot I achieve the last 10-20MiB/s in performance on the Atom board?

Also, the other direction (READ) I get 105-110MiB/s:
procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu----
 r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa
 0  0      0  37260    328 3888560    0    0  3187  6746 2295  309  1 13 84  1
 0  0      0  36632    328 3890492    0    0 105184     0 23332 4924  3 21 75  0
 0  0      0  35516    328 3893688    0    0 105616     0 23567 5143  3 22 75  0
 1  0      0  35888    328 3894428    0    0 106404     0 23247 5167  3 21 76  0
 0  0      0  35392    328 3897068    0    0 106472     0 23351 5221  3 21 76  0

What is causing the bottleneck for write?

Justin.

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