installed high sierra on external SSD, formatted as APFS and it created a 2nd/intermediate container. is this right? also what is vm/swapfile0?

[chestbox]

greetings people. i have a late 2012 imac, and just did a clean install for high sierra on an external SSD. i formatted it as APFS (think it's recommended for SSDs) and installed OS.

now when looking at disk utility, and select 'show all devices', the above is the internal HHD, currently not being used, formatted as mac os extended journaled, but for the external, formatted in APFS, it has the intermediate 'container disk2'. since i've never seen this before, and i'm not sure if this is to be expected, i'd really like to make sure i've done everything right.

additionally, in the macSSD folder, next to the folders: applications, library, system & users, I also have a folder called vm with a 1.07gb textfile called 'swapfile0'. after a quick google, i understand that this has to do with ram offloading? i'm not sure what this means, but does it make sense for this to appear after a fresh install?

thanks in advance

 

[gilby101]

That is completely normal.

APFS:
The disk is partitioned with, by default, two partitions. The boot partition called EFI and an APFS container. You can see both with the terminal command diskutil list. Disk Utility hides stuff that we maybe don't need to see.

The APFS container contains volumes. One of the volumes is your system volume which you have called Macintosh SSD. Again diskutil list will show some other volumes: Preboot, Recovery and VM.

VM:
When you fill your RAM with macOS and applications, the operating system takes steps to free up some RAM when needed. Some application data (of very idle apps and services) is written to the disk in one or more 'swapfiles'. It will be read back when needed again.

This is what you are seeing in the folder vm (named for virtual memory) where there can be multiple swapfiles created as needed. The first one is 1GB in size.

What complicates things is that this vm folder is not really part of the macOS system volume. It is located in a separate APFS volume called VM which is shown by diskutil list.

 

[chestbox]

thank you so much for the clarification and detailed explanation.
checked diskutil list, despite honestly not knowing what to do with all the information. just appreciate that everything appears to be as expected, and i'm guessing i should not really care about virtual memory either.
thanks again!!