I have a hardware raid array in an HP Proliant ml350 server. I have 2 logical drives. Drive "C" has three 67.5 SCSI drives in a raid 1 configuration and Drive "D" has two 67.5 drives in a Raid 0 configuration. Can I start swapping the raid 1 drives for larger drives and if so, how long does it take for the mirror to occure?
Before you jump into it, make sure that the RAID controller supports expansion (online expansion). If it doesn't, you're wasting your time as you'll have to nuke the array in order to make it bigger anyway.
Second point - if you're running RAID0, you can't expand this array, or any arrays that share disks with it. The second you remove a drive it's all over. In fact RAID0 should not be called RAID at all. Just AID. There's no redundancy so you won't be touching this array without destroying it.
So, if your RAID1 array shares disks with your RAID0 array, you can't do it.
Third point - how can your RAID1 have only three disks? RAID10 is four disks. If you have three disks, then it's probably actually RAID5. Not that this makes any difference.
If your RAID0 array is completely independent of your RAID1 array, AND your controller supports expanding the array, then you should be OK. I highly recommend making a backup of everything just in case.
As for how long it will take to rebuild the array, how long is a piece of string? The more stress the server is under the longer it will take to rebuild. I know of a 14-disk array that took more than a week to rebuild because of the immense I/O stress it was under. The only way to know for sure is to do it. I would guess about 12 hours based on previous experience with disks of this capacity on a server that's in use.