open_sync fails

Basic system setup:

Linux 2.4 kernel (heavily modified)
Dual core Athlon Opteron
4GB ECC RAM
SW RAID 10 configuration with 8 750 Gb disks (using only 500Gb of each
disk) connected via LSISAS1068 based card

While working on tuning my database, I was experimenting with changing
the wal_sync_method to try to find the optimal value. The really odd
thing is when I switch to open_sync (O_SYNC), Postgres immediately fails
and gives me an error message of:

2008-07-22 11:22:37 UTC 19411 akamai [local] PANIC: could not write to
log file 101, segment 40 at offset 1255
8336, length 2097152: No space left on device

Even running the test_fsync tool on this system gives me an error
message indicating O_SYNC isn't supported, and it promptly bails.

So I'm wondering what the heck is going on. I've found a bunch of posts
that indicate O_SYNC may provide some extra throughput, but nothing
indicating that O_SYNC doesn't work.

Can anybody provide me any pointers on this?

Thanks

--Rick