I would like to replace the two internal 160 GB HDs in my PowerMac dual 1,8GHz PPC. Originally, I was looking for two identical HDs for a software RAID-0 and an external HD for backup (time machine). However, considering the massive storage sizes of disks nowadays, I am thinking of a 300 GB WD Velociraptor as the main boot disk, and a 1TB WDC Black as the backup disk. These two HDs have the same transfer rate (3 Gb/s), but differ in RPM (10,000 RPM vs. 7,2000 RPM) and cache (16 MB vs. 32/64 MB). Is it OK to have such internal setup? Or will the "slower" HD affect overall performance? If it is OK, can I partition the 1TB internal HD to use one portion for Time Machine and the other one for pure direct storage? For instance, I would like to use Time Machine for everything except my music and photo libraries and the rest of the disk to hold a duplicate copy of my libraries. Thanks!