Write barriers and hardware RAID

[J Pälve]

Hi,

I'm setting up a server to provide storage for a couple of VMware ESXi 
servers. I'm using the latest stable Debian and I'm leaning towards using 
NFS with XFS. However, I'm concerned about data integrity in the event of 
power-out (we have UPS but they only last so long). Here are the specific 
questions I have:

- The XFS FAQ states that with battery backup'd RAID hardware, both write 
barriers and individual disk cache should be turned off. However, I'm 
getting better benchmark results with both turned on. What I'm wondering 
is, will write barriers work as intended when used with hardware RAID 
controller (PERC 6/E)? Googling only turned up results relating to 
software RAID.

- The XFS FAQ also states that virtualization products prevent write 
barriers from working correctly. Is this still the case (specifically with 
ESXi 3.5 and later) and is there anything that can be done about it? Does 
VMFS somehow work around this, or is the problem then just "out of sight, 
out of mind"?

Bregs,
   JPa