With Intel Matrix Storage manager, you can create a RAID1 mirror from two drives online, using one (old) drive as a source and the new one as target. It will sync in the background for several hours, making your disk access slower during that time, and that's about it. No need to reformat, repartition, etc.
You can use any disk, provided its size is equal or larger than the original disk, and the new disk is connected to the same SATA controller on your motherboard. Manufacturer of a disk does not matter. Moreover, it is often suggested to buy a different model disk, so if there is a systematic problem with certain disk model (like it was with Seagate disks not too long ago), at least one of the disks in your RAID would not be affected.
Sometimes same-capacity different model disks (e.g. 1TB) differ in their actual size by a few sectors. I've never had problem creating RAID1 mirrors from, say, 1TB WD and Seagate disks (with Intel Matrix Storage).
One other potential problem is the sector size. Some newer disks use 4KB sector size, while older disks all use 512 bytes sector size. I don't know how Intel Matrix storage would cope with different-sector-size disks, and what performance implications might be, but I suppose it's better to stick to same-sector-size disks. Check your disk, it is most probably has 512bytes sectors.
Do you what will happen if the new disk is a few sectors smaller than the original one? Will I have to some resize (e.g. repartition) the original one so that it can be fully mirrored, or will the Intel controller somehow handle this automatically? – Suma – 2012-01-17T09:05:11.183
I think the firmware handles this somehow (e.g. this is just a few sectors and they do not matter, partitions do not go to the very end, etc.)... I've never had problems with this issue with Intel Matrix, but since I'm not 100% sure, I didn't want to include this into my answer. In any case, the size of RAID1 array will be the size of the smallest disk included in it, not larger. – haimg – 2012-01-17T14:41:37.057