pg_xlog safety

I reconfigured my database server this weekend based on some notes
posted here.  What I did was change the 5-disk RAID5 into a 4-disk
RAID10 plus one spare drive.

Now, this should have made things much faster, but from the looks of
it, I'm not so sure it got faster.  Reindexing the dump after loading
the data took *way* longer than I expected.  However, now that it is
reindexed and vacuum analyzed, things do appear faster.  I'm not sure
if that's just from having the indexes rebuilt or what...

So this leads me to my question: one of the tips for performance is to
move the pg_xlog to its own disk.  Now that I have a spare disk I was
considering moving pg_xlog there.  However, that's the only disk that
wouldn't be RAID protected.  What would happen to the db if that disk
failed?  If I were able to perform a clean shutdown, replace that
disk, and start up postgres again, would it be ok with the pg_xlog
directory empty?  Is it only used for startup after an unclean
shutdown or for every startup?


--
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Vivek Khera, Ph.D.                Khera Communications, Inc.
Internet: khera@kciLink.com       Rockville, MD       +1-240-453-8497
AIM: vivekkhera Y!: vivek_khera   http://www.khera.org/~vivek/