I have installed Ubuntu on a DELL 2850 and I have configured an array of 5 disks (SCSI 73GB 10K) in RAID5.

I wanted to simulate a drive error so in the middle of something I just took one of the drives out and put it back again after a bit. Then the drive shows an orange light and seems to be rebuilding but actually is taking hours and hours with no results. So I went to the PERC utility (Ctrl+M) and the disk shows "REBLD". But it never gets to an online state. So I went to Objects - Physical drives - Rebuilding - View rebuild process. And in here I can see a bar moving from 0%... but if I reboot before finishing and get into the PERC Utility again, it seems to start again rebuilding from 0% - so it is not rebuilding automatically.

My concern is: what would happen in a real situation? Do I have to just switch the server off and go to the Perc utility to start the rebuilding manually? I thought the whole point was to have this done automatically and without the need of stopping the server. Or does it perhaps rebuild automatically indeed but needs to have enough time without rebooting because otherwise the rebuilding process will start from scratch? It seems to take more than 3h for a 73gb disk!

My second question is: can I mix then hard drives? So if I have a RAID of 5x73GB 10K can I use different size (146GB) or speeds (15K)? Apparently someone said it is OK in here Poweredge 2850: replace disk with larger in RAID?