Chosen Solution
I have my old MacBook Pro that has 10.6.4 Snow Leopard just if I want to mess around + to run old software, but now I also need it to host a “server” (if you could call it that) - so I need 10.13 High Sierra on it. Problem is, I don’t want to go through those 8 hours of installing 10.6 on this computer again + I may need to use that older software again, so I want to have one partition be 10.6 and the other be 10.13. Would it be possible even with 10.13 using the APFS file format? I know absolutely nothing about software - so sorry if this sounds like a rather dumb question.
Your system really can’t support APFS. APFS is a very chatty file system unlike HFS+ (Journaled File System) so you loose performance and run into SATA cache issues. SATA based systems should stick with HFS+ running Sierra. High Sierra is an odd duck! It was the first release of APFS and Apple has already gone to the third version (Big Sur I think is running something still newer!). Remember your system is also running SATA II (3.0 Gb/s) so its not the fastest HDD and even if you had upgraded it to an SSD won’t leverage what the drive can offer. So setting up HFS+ is your best option or better yet setup a second drive and just levered the Startup Manager using the Option (⌥) key Reference: Mac startup key combinations
