I have set raid 0 with 2 identical hdd 640gb, there is still room for 2 more hdd, is it ok if we install one 320gb hdd without making it raid, u understood my question right 2 hdds for raid and 1 for jbod. will it work
If you just install the 3rd drive on it's own you will be fine. Leave the raid array alone and install the drive as JBOD will not be necessary as you don't have more drives present. You cannot add the drive to your raid 0 array. The drive will show up as a separate drive on it's own. If you want to have a JBOD set up your chipset must support it and you will have to loose your raid0 set up (loosing the data as well your performance from the raid 0 set up) IMHO there would be no advantage to set up the system to have a JBOD set up.
It is possible to do what you want but as shabaa said, just leave the 3rd out of any RAID configuration and leave it as a single drive (ie not set to RAID in bios).
I have a simialr configuration in one of my machines, 2x80GB (maxtor) in a RAID 0 (c: OS and a 500GB (WD) (d: for documents etc) and a 250GB (seagate)(e: backups of critical files) as separate drives and everything works fine.
my hdd are
slot1: western digital caviar green 640GB
slot2: western digital caviar green 640GB
these are in raid 0
i want to insert one more non raid HDD at
slot 3: seagate 320gb hdd
is it possible, 2 hdd being raid but one not
yes. it is possible. when you add the 3rd drive, do NOT redo the raid. if you have any option at all, it should ask you if you want to redo your raid0 for all three drives, and when you say no, it should default to "normal" for the 3rd drive; which is what you want. you dont want it in a raid at all; so i dont think it'll give you a JBOD option. you need two or more drives to have jbod, and you are only adding one.