Why do we see a big performance/load difference between ext3 and ext4 using the same hardware (RHEL5 and RHEL6)?

Solution Unverified - Updated -

Issue

When running the same file system load test (read/write) on a ext3 and ext4 file system we see a big difference on the load of the system, especially when running a sync while the load test is running.

  • RHEL6+ext3:
# time sync

real    13m32.737s
user    0m0.002s
sys     0m0.056s
  • RHEL5+ext3:
# time sync

real    12m1.334s
user    0m0.000s
sys     0m0.833s

The bad sync timer are related to the high load of the machine:

top - 14:30:58 up 56 min,  5 users,  load average: 46.08, 34.01, 22.04
Tasks: 383 total,   1 running, 382 sleeping,   0 stopped,   0 zombie
Cpu(s):  0.5%us,  0.3%sy,  0.0%ni, 74.4%id, 24.8%wa,  0.0%hi,  0.0%si,  0.0%st

top - 14:31:37 up 57 min,  5 users,  load average: 57.96, 38.29, 23.90
Tasks: 382 total,   1 running, 381 sleeping,   0 stopped,   0 zombie
Cpu(s):  0.9%us,  1.2%sy,  0.0%ni, 37.9%id, 60.0%wa,  0.0%hi,  0.0%si,  0.0%st

Running the same test on the exact same hardware using ext4 the load is low and the sync performance is good:

top - 17:14:55 up  2:43,  6 users,  load average: 0.53, 0.52, 5.73
Tasks: 344 total,   2 running, 342 sleeping,   0 stopped,   0 zombie
Cpu(s):  1.1%us,  2.9%sy,  0.0%ni, 42.9%id, 52.9%wa,  0.0%hi,  0.2%si,  0.0%st


# time sync

real    0m2.510s
user    0m0.000s
sys     0m0.127s

Running same tests on a bigger system with RHEL6+ext3 we can see that the performance is good:

processor   : 63
vendor_id   : GenuineIntel
cpu family  : 6
model       : 45
model name  : Intel(R) Xeon(R) CPU E5-4650 0 @ 2.70GHz

# cat /proc/meminfo 
MemTotal:       65880916 kB
# time sync

real    0m19.530s
user    0m0.000s
sys     0m0.141s

Why is there so a big difference in the load of the machine using ext3 or ext4 file system?

Environment

  • Red Hat Enterprise Linux 6.3
  • Red Hat Enterprise Linux 5.8

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