Its better to split WAL segments and data just because these two have different io requirements and because its easier to measure and tune things if you have them on different disks.
raid0 tends to linear scaling so 3 of them should give something close to 300% increased write speed. So i would say 1. but make sure you test your configuration as soon as you can with bonnie++ or something similar
I have a server with 32GB ram, one intel E3-1245 and four 15k SAS disks with a BB LSI MegaRaid controller. I wan't the optimal performance for my server, which will be pretty write heavy at times, and less optimized for redundancy, as my data is not very crucial and I will be running a streaming replication along side.
Now what would you prefer:
1) 3 disks in RAID 0 containing PGDATA + 1 containing SYSTEM and WAL 2) All four in RAID 10 containing both PGDATA, SYSTEM AND WAL 3) 2 disks in RAID 1 containing PGDATA + 2 disks in RAID 1 containing SYSTEM and WAL 4) Something different?
A 5. option could also be to simply have all 4 disk in a RAID 0 containing all PGDATA, SYSTEM and WAL
