We have the following hardware configuration
Dell 1750 1U
Dual Xeon 3.06 Ghz
2 GB Ram
3 x 73GB - 15000-RPM SCSI Drives
Hardware Raid

I know RAID 10 is recommend everywhere and RAID 5 is not, but with 3 dives only RAID 10 is not an option and we want stable/fault tolerant system.

So what kind of RAID and OS Partitions can we have for Zimbra OSS server which will be loaded with 300-400 POP3/SMTP users and 20-50 web mail users, no IMAP, calendaring is not used by 97% of the users but is enabled in the system, AV/AS is enabled.

What options of the following are best? Performance is not the top most priority but stability and fault tolerance is.

Raid Options:
Option 1: RAID 5

Option 2:
Disk 1: No RAID and will have OS on it
Disk 2 and Disk 3: RAID 1 with /opt on it to have all Zimbra files

* If RAID 5 is slow in writing how much it will degrade the performance in terms of % compared to RAID 10

OS Partition Options for CentOS 5.x