unable to expand raidgroup - lost disk

Spud,
As long as the RAID group is a RAID 10, 5, or 0 (who uses those?), the Expand button should be available on the RAID group properties. Unless you have already reached the maximum number of disks for the RAID group, which is 16. If you are adding to a RAID 10 it has to be in multiples of two, you can only add single disks to a RAID5 or RAID0 group.

What is the disk type of the RAID group and the disk that you want to add? If you are trying to add an ATA disk to a FC RAID group or vice versa, then the disk will not be available. Also best practices dictate that you add the same capacity or larger disk, and of the same RPM.

Aran

and you cant use it as a hot spare too

Well it's a raid 5 group which contains only 3 disks. i can add another disk to it, but my problem is that i can't see only 1 disk.

disks 0,1,2 are in the raid group, all FC disks (don't have any others) all 300GB, i can expand the raidgroup with disknumber 4, but disknumber 3 just isn't visible when i choose expand. like i said the diskstate is unbound so isn't part of any other raidgroup.

i know the OS of the CX500 is also on these disks..but that shouldn't be the issue.

all my other disks are already taken by other raidgroups..

.........very weird..

you cant use the first 5 disks to expand a RAID group thats made up by remaining disks on the array, even if the disk capacity is same. usable capacity of the first five disks is less than the other disks due to OS space (few GBs).
you can expand the RG on first five disks using any other same sized/type disks though.