New APFS volume seems to be showing incorrect remaining size

[madihavu]

I've been using a 2TB USB drive for Time Machine backup, I decided to carve out 500GB in a new volume as separate temporary storage, but when I click on it in Finder (on the left side under Locations), it shows 1.64 TB available... when I click on the base drive that the volume came from (which also has the Time Machine backup), it says 1.14 TB available... which obviously add up to more then 2TB.

When I look again at the drive in Disk Utility, the original "volume" (?) says Used 364.64 GB (the automated backups), Other Volumes --, Free 1.14 TB; the new volume says Used 133.7 MB (500 GB reserve) (which contains files I just moved over), Other Volumes --, Free 1.63 TB.

So I'm not understanding how the Mac is thinking about remaining space on these "volumes" (I'm not sure what they're actually called, but I'm used to partitions on Windows).

Ultimately I'd like to be able to access the separate temporary storage on any computer should the Mac fail or become lost somehow, but I don't know yet if this will work on older/newer/different Macs or Windows.

 

[Cory Cooper]

Hello and welcome.

The APFS file system uses containers (partitions) and volumes. It is far different from older disk hierarchies.

Disk Utility User Guide

• Partitioning a disk divides it into individual sections known as containers.
• Apple File System (APFS) allocates disk space on demand. When a single APFS container (partition) has multiple volumes, the container’s free space is shared and can be allocated to any of the individual volumes as needed. Each volume uses only part of the overall container, so the available space is the total size of the container, minus the size of all volumes in the container.
• On your computer, macOS is installed on a set of volumes known as a volume group. The volume group consists of one volume used for the system files (named Macintosh HD) and another volume used for data (named Macintosh HD - Data).

Basically, it sounds like it is reporting free space correctly, as the different containers (partitions) can share the available space. Does that help?

C

 

[madihavu]

I tried to understand that blurb you mentioned (I saw it before), and it either sounds like gobbledygook to me or is overly-complicated. I don't understand its benefit over typical partitioning, nor how to determine actual free space without having an idea of how much I already have on it to begin with.

I understand that APFS may store file metadata that exFAT can't, but I don't know if that's enough benefit to use APFS over exFAT when my other computers are Windows (and I don't use iPhone though I have an iPad).

All I understand is: How much free space does a drive/partition (container? volume? aaahhh) have? Is it necessary for me to understand APFS' complicated explanation to get a simple X amount of free space left?

Right now just a glance at the drive/partition/container/volume/wtf has significantly different numbers for remaining space depending on where I look; like, it's not just a megabyte/mibibyte thing, this is a whole new dimension of differing numbers.

Regardless, Disk Utility reports two different numbers for Free xGB... whatever the explanation is, the display or names of these numbers on its face is contradictory, so maybe Apple's just made a poor design decision here.