Based on the pic, it's definitely a PERC card (PowerEdge Expandable RAID Controller). What's in question is which PERC card it is. Reboot the system and press CTRL+M when you see this message to go into the controller configuration utility, which may identify the card for you. Short of that, and barring any other information displayed during POST, you may need to remove the card in order to identify it visually.
PERC 6i is LSI gear, so in general anything that goes with the MegaRAID SAS controllers, will work on the Dell PERC.
We can add a disk to the array one at a time, and the controller will expand the array
You will notice this not to be the case. Just adding the drives will make them available for the use in a new container, but not automatically grow anything. You should be able to use the Dell OpenManage tools to add the disk to the array as a replacement for a defective or offlined disk - the array will regenerate by writing redundant data to that disk.
What we do not know is what happens
when ALL the drives have been
replaced, and are now 450Gb drives,
does the RAID controller automatically
grow the array to use all 450Gb on
each of the disks or will we end up
with 50Gb wasted space on each drive?
At first, it is the latter - your array will be the same size with unused space on each of its disks. But you might try to expand your virtual disk using OpenManage Storage Manager. Please note that the expansion of the virtual disk will not expand your partitions and filesystems contained there. You will need additional software to do that - a GParted live CD should cope with most resizing needs and will support your controller out-of-the-box.
will the controller allow us to then
create a new RAID 5 array using these
6 x 50Gb spaces
Yes, but you should only do this if the disk expansion is infeasible for some reason.
With all that said, it is a complex operation which might fail and take all data with it at any stage, so having a backup which can be restored swiftly (e.g. a full disk image) is strongly advisable.
Best Answer
One of two things:
The card will have disabled the write cache which will have a hefty impact on performance. I believe this is the case for most latter day PERC firmwares.
If the write cache is still enabled, then you should disable it, because in the event of sudden loss of power (power cut or hard reboot) you may lose data that hasn't yet been committed to disk.
It's advisable to purchase a Battery Backup Module for the card. You can pick up one for that particular model quite cheap - especially on Ebay, if you're that way inclined.