[CentOS] Ideal RAID-1 Stripe Size for IMAP Server ?

Hi there.

I'm currently configuring a brand new email server(IMAP) which will run
CentOS 6.3 x64. 

So lots of files on the data volume.

I'm confused about stripe size for my data volume.
I'm using 2x500GB for OS in RAID1 and 2x2TB SAS for DATA in RAID1 which is
hosted on a HP Smart Array P420 Controller with 1GB in Cache/Battery Backed Up.
Both these array's are on the P420 controller.

The initial configuring from Array Configuration Tools gives me 256K in Strip Size.
On both array's. 

What would be ideal for the data volume, and or the OS array ?

I'm going to run XFS for the DATA volume.

Any help and or suggestions would be much appreciated.

Thanks allot folks.

Best regards,

Svavar
Reykjavik - Iceland