I just got hold of a new Maxtor 120GB HD for the special price of HK$777 (plus any old HD to trade in, which I have a couple lying around), and installed it into marilyn my home server to replace the dead 40GB. I was reluctant to do this with a 120GB, ‘cos althou it would work, the 80GB of left over space on the new HD will not form part of the RAID. It will be pretty much wasted.
Then I realized that this wouldn’t be the case, as the wastage will only be temporary. The older 40GB will likely be the next to die. If not it will still eventually die. Then I’ll just replace it with a new 120GB HD, build an additional RAID partition with the free space on the pair of HDs, then move the /home directory over to the newly formed (and much larger) RAID partition. So in the future whenever a HD dies I put in a new HD about twice the size of the bigger HD in the RAID. This way I stay somewhere close to the sweet spot of good price-performance ratio, and the RAID has a chance to grow.
I started the rebuilding about two hours ago, and it’s about half finished. No service interruption except power down the server to install the new HD.