Aaaand, this is why you should be running OS 8 or later.
Yes, the short answer is that no, your files aren't magically going to expand to fill the allocation block size; when the system reads one it'll stop when it gets to the EOF, so you're not going to see some huge jump in RAM use. Possibly more relevant, however: HFS limits you to a total maximum of 65,535 files. That's... possibly a genuine problem when you're talking about a 1TB+ hard disk. If you assume, for instance, a roughly average size of 3MB each that's "only" about 200GB worth of MP3s...
Which raises an interesting point, actually. The math suggests that if your minimum file size is coming out to 30MB-ish you have closer to a 2TB drive *or* that your drive is just barely over 1TB and HFS has to make the minimum allocation block a power of 2. I'm too lazy to figure out which that is, actually. (The wording on Wikipedia's page on HFS says "the limit of 65,535 allocation blocks resulted in files having a "minimum" size equivalent 1/65,535th the size of the disk", and 1TB divided by 65535 would be 16MB. However, I know with the DOS FAT16 filesystem, which has similar limitations, block sizes have to be an even power of two, IE; if you have a 1GB disk you have 16k clusters, but at 1GB+32k it'll switch to 32k clusters.)
I do suggest you read the other parts of the Wikipedia article on HFS, specifically the part where it talks about its fragility. Seriously, it's not a good basket to keep your eggs in.
Yes, the short answer is that no, your files aren't magically going to expand to fill the allocation block size; when the system reads one it'll stop when it gets to the EOF, so you're not going to see some huge jump in RAM use. Possibly more relevant, however: HFS limits you to a total maximum of 65,535 files. That's... possibly a genuine problem when you're talking about a 1TB+ hard disk. If you assume, for instance, a roughly average size of 3MB each that's "only" about 200GB worth of MP3s...
Which raises an interesting point, actually. The math suggests that if your minimum file size is coming out to 30MB-ish you have closer to a 2TB drive *or* that your drive is just barely over 1TB and HFS has to make the minimum allocation block a power of 2. I'm too lazy to figure out which that is, actually. (The wording on Wikipedia's page on HFS says "the limit of 65,535 allocation blocks resulted in files having a "minimum" size equivalent 1/65,535th the size of the disk", and 1TB divided by 65535 would be 16MB. However, I know with the DOS FAT16 filesystem, which has similar limitations, block sizes have to be an even power of two, IE; if you have a 1GB disk you have 16k clusters, but at 1GB+32k it'll switch to 32k clusters.)
I do suggest you read the other parts of the Wikipedia article on HFS, specifically the part where it talks about its fragility. Seriously, it's not a good basket to keep your eggs in.