Two identical systems, radically different performance

This is driving me crazy. A new server, virtually identical to an old one,
has 50% of the performance with pgbench. I've checked everything I can
think of.

The setups (call the servers "old" and "new"):

old: 2 x 4-core Intel Xeon E5620
new: 4 x 4-core Intel Xeon E5606

both:

memory: 12 GB DDR EC
Disks: 12x500GB disks (Western Digital 7200RPM SATA)
2 disks, RAID1: OS (ext4) and postgres xlog (ext2)
8 disks, RAID10: $PGDATA

3WARE 9650SE-12ML with battery-backed cache. The admin tool (tw_cli)
indicates that the battery is charged and the cache is working on both
units.

Linux: 2.6.32-41-server #94-Ubuntu SMP (new server's disk was
actually cloned from old server).

Postgres: 8.4.4 (yes, I should update. But both are identical.)

The postgres.conf files are identical; diffs from the original are:

max_connections = 500
shared_buffers = 1000MB
work_mem = 128MB
synchronous_commit = off
full_page_writes = off
wal_buffers = 256kB
checkpoint_segments = 30
effective_cache_size = 4GB
track_activities = on
track_counts = on
track_functions = none
autovacuum = on
autovacuum_naptime = 5min
escape_string_warning = off

Note that the old server is in production and was serving a light load
while this test was running, so in theory it should be slower, not faster,
than the new server.

pgbench: Old server

pgbench -i -s 100 -U test
pgbench -U test -c ... -t ...

-c -t TPS
5 20000 3777
10 10000 2622
20 5000 3759
30 3333 5712
40 2500 5953
50 2000 6141

New server
-c -t TPS
5 20000 2733
10 10000 2783
20 5000 3241
30 3333 2987
40 2500 2739
50 2000 2119

As you can see, the new server is dramatically slower than the old one.

I tested both the RAID10 data disk and the RAID1 xlog disk with bonnie++.
The xlog disks were almost identical in performance. The RAID10 pg-data
disks looked like this:

Old server:
Version 1.96 ------Sequential Output------ --Sequential Input-
--Random-
Concurrency 1 -Per Chr- --Block-- -Rewrite- -Per Chr- --Block--
--Seeks--
Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec
%CP
xenon 24064M 687 99 203098 26 81904 16 3889 96 403747 31
737.6 31
Latency 20512us 469ms 394ms 21402us 396ms
112ms
Version 1.96 ------Sequential Create------ --------Random
Create--------
xenon -Create-- --Read--- -Delete-- -Create-- --Read---
-Delete--
files /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP /sec
%CP
16 15953 27 +++++ +++ +++++ +++ +++++ +++ +++++ +++ +++++
+++
Latency 43291us 857us 519us 1588us 37us
178us
1.96,1.96,xenon,1,1349726125,24064M,,687,99,203098,26,81904,16,3889,96,403747,31,737.6,31,16,,,,,15953,27,+++++,+++,+++++,++\
+,+++++,+++,+++++,+++,+++++,+++,20512us,469ms,394ms,21402us,396ms,112ms,43291us,857us,519us,1588us,37us,178us

New server:
Version 1.96 ------Sequential Output------ --Sequential Input-
--Random-
Concurrency 1 -Per Chr- --Block-- -Rewrite- -Per Chr- --Block--
--Seeks--
Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec
%CP
zinc 24064M 862 99 212143 54 96008 14 4921 99 279239 17
752.0 23
Latency 15613us 598ms 597ms 2764us 398ms
215ms
Version 1.96 ------Sequential Create------ --------Random
Create--------
zinc -Create-- --Read--- -Delete-- -Create-- --Read---
-Delete--
files /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP /sec
%CP
16 20380 26 +++++ +++ +++++ +++ +++++ +++ +++++ +++ +++++
+++
Latency 487us 627us 407us 972us 29us
262us
1.96,1.96,zinc,1,1349722017,24064M,,862,99,212143,54,96008,14,4921,99,279239,17,752.0,23,16,,,,,20380,26,+++++,+++,+++++,+++\
,+++++,+++,+++++,+++,+++++,+++,15613us,598ms,597ms,2764us,398ms,215ms,487us,627us,407us,972us,29us,262us

I don't know enough about bonnie++ to know if these differences are
interesting.

One dramatic difference I noted via vmstat. On the old server, the I/O
load during the bonnie++ run was steady, like this:

procs -----------memory---------- ---swap-- -----io---- -system--
----cpu----
r b swpd free buff cache si so bi bo in cs us sy id
wa
r b swpd free buff cache si so bi bo in cs us sy id
wa
0 2 71800 2117612 17940 9375660 0 0 82948 81944 1992 1341 1 3
86 10
0 2 71800 2113328 17948 9383896 0 0 76288 75806 1751 1167 0 2
86 11
0 1 71800 2111004 17948 9386540 92 0 93324 94232 2230 1510 0 4
86 10
0 1 71800 2106796 17948 9387436 114 0 67698 67588 1572 1088 0 2
87 11
0 1 71800 2106724 17956 9387968 50 0 81970 85710 1918 1287 0 3
86 10
1 1 71800 2103304 17956 9390700 0 0 92096 92160 1970 1194 0 4
86 10
0 2 71800 2103196 17976 9389204 0 0 70722 69680 1655 1116 1 3
86 10
1 1 71800 2099064 17980 9390824 0 0 57346 57348 1357 949 0 2
87 11
0 1 71800 2095596 17980 9392720 0 0 57344 57348 1379 987 0 2
86 12

But the new server varied wildly during bonnie++:

procs -----------memory---------- ---swap-- -----io---- -system--
----cpu----
r b swpd free buff cache si so bi bo in cs us sy id
wa
0 1 0 4518352 12004 7167000 0 0 118894 120838 2613 1539 0 2
93 5
0 1 0 4517252 12004 7167824 0 0 52116 53248 1179 793 0 1
94 5
0 1 0 4515864 12004 7169088 0 0 46764 49152 1104 733 0 1
91 7
0 1 0 4515180 12012 7169764 0 0 32924 30724 750 542 0 1
93 6
0 1 0 4514328 12016 7170780 0 0 42188 45056 1019 664 0 1
90 9
0 1 0 4513072 12016 7171856 0 0 67528 65540 1487 993 0 1
96 4
0 1 0 4510852 12016 7173160 0 0 56876 57344 1358 942 0 1
94 5
0 1 0 4500280 12044 7179924 0 0 91564 94220 2505 2504 1 2
91 6
0 1 0 4495564 12052 7183492 0 0 102660 104452 2289 1473 0 2
92 6
0 1 0 4492092 12052 7187720 0 0 98498 96274 2140 1385 0 2
93 5
0 1 0 4488608 12060 7190772 0 0 97628 100358 2176 1398 0 1
94 4
1 0 0 4485880 12052 7192600 0 0 112406 114686 2461 1509 0 3
90 7
1 0 0 4483424 12052 7195612 0 0 64678 65536 1449 948 0 1
91 8
0 1 0 4480252 12052 7199404 0 0 99608 100356 2217 1452 0 1
96 3

Any ideas where to look next would be greatly appreciated.

Craig