further testing on IDE drives

I was testing to get some idea of how to speed up the speed of pgbench
with IDE drives and the write caching turned off in Linux (i.e. hdparm -W0
/dev/hdx).

The only parameter that seems to make a noticeable difference was setting
wal_sync_method = open_sync. With it set to either fsync, or fdatasync,
the speed with pgbench -c 5 -t 1000 ran from 11 to 17 tps. With open_sync
it jumped to the range of 45 to 52 tps. with write cache on I was getting
280 to 320 tps. so, not instead of being 20 to 30 times slower, I'm only
about 5 times slower, much better.

Now I'm off to start a "pgbench -c 10 -t 10000" and pull the power cord
and see if the data gets corrupted with write caching turned on, i.e. do
my hard drives have the ability to write at least some of their cache
during spin down.