The use of nobarrier provides a great performance gain on my laptop. I thinki I will continue like that even if my hard drive has got not battery unit.
With ext4 (rw,noatime,errors=remount-ro,data=ordered)
#fs_mark -t 4 -s 10240 -n 1000 -d /home/goneri/tmp/test
# Version 3.3, 4 thread(s) starting at Mon Feb 4 10:35:47 2013
# Sync method: INBAND FSYNC: fsync() per file in write loop.
# Directories: no subdirectories used
# File names: 40 bytes long, (16 initial bytes of time stamp with 24 random bytes at end of name)
# Files info: size 10240 bytes, written with an IO size of 16384 bytes per write
# App overhead is time in microseconds spent in the test not doing file writing related system calls.
FSUse% Count Size Files/sec App Overhead
o 84 4000 10240 35.2 113031
ext4 (rw,noatime,nobarrier,errors=remount-ro,commit=15,data=ordered)
tosh-r630:/tmp$ fs_mark -t 4 -s 10240 -n 1000 -d ~/tmp/test
# fs_mark -t 4 -s 10240 -n 1000 -d /home/goneri/tmp/test
# Version 3.3, 4 thread(s) starting at Mon Feb 4 10:40:06 2013
# Sync method: INBAND FSYNC: fsync() per file in write loop.
# Directories: no subdirectories used
# File names: 40 bytes long, (16 initial bytes of time stamp with 24 random bytes at end of name)
# Files info: size 10240 bytes, written with an IO size of 16384 bytes per write
# App overhead is time in microseconds spent in the test not doing file writing related system calls.
FSUse% Count Size Files/sec App Overhead
84 4000 10240 839.9 99672