IOS – What do the partitions /dev/disk1s* in filesystem mean (disk storage management)

iosstorage

When U run df -h I get the following output (formatted as table for better viz).
What do all these /dev/disk1s* mean? Can it be that I lose space due to some imposed partition?

Filesystem Size Used Avail Capacity Mounted on
/dev/disk1s5s1 233Gi 14Gi 22Gi 40% /
devfs 193Ki 193Ki 0Bi 100% /dev
/dev/disk1s4 233Gi 5.0Gi 22Gi 19% /System/Volumes/VM
/dev/disk1s2 233Gi 320Mi 22Gi 2% /System/Volumes/Preboot
/dev/disk1s6 233Gi 1.0Mi 22Gi 1% /System/Volumes/Update
/dev/disk1s1 233Gi 192Gi 22Gi 90% /System/Volumes/Data
map auto_home 0Bi 0Bi 0Bi 100% /System/Volumes/Data/home

My OS version is BigSur (11.2.2)

Best Answer

The disk1s* in /dev/disk1s* are identifiers for the APFS volumes and snapshot in the container with the identifier disk1. These are not partitions as stated in your question. The APFS container resides in either a single partition on a drive or two partition on separate drives. In your example, the APFS volumes and snapshot all share in the same APFS container. Below shows the sum of the volumes, snapshot and available space equal the APFS container size. There is no lost of space.

 disk1s5s1    14. Gi
 disk1s4       5. Gi
 disk1s2       0.320 Gi
 disk1s6       0.001 Gi
 disk1s1     192. Gi
 disk1s3        .569 Gi
 Available    22. Gi
           ------------
 Size        233. Gi

Note: You did not include in your question the size of the unmounted Recovery volume (disk1s3). The value of 569 MiB came from my Big Sur installation. This value should be the same on your Big Sur installation.

Below was taken from man diskutil. I edited out the text that does not directly relate to the OP's question.

You are referring to disk identifiers. In your example, the (BSD) disk identifier string variously identifies a virtual logical volume. It will take the form of diskCsV, or diskCsVsS where C, S, and V are positive decimal integers (possibly multi-digit), and where:

  • C is an APFS Container. This is a virtual disk constructed by APFS to represent a collection of APFS Volumes. Multiple APFS Containers can be active simultaneously.
  • V is an APFS Volume; it refers to a virtual logical volume that is shared out of an APFS Container. For example, exported from an APFS Container designated as disk1 there might be an APFS Volume disk1s1, mountable as a file system and usable for file storage via its mountpoint path.
  • S is an APFS Snapshot; it refers to a frozen moment in time of the state of files on an APFS Volume. For example, if APFS Container disk6 has an APFS Volume disk6s3, and two APFS Snapshots have been "taken" on it, these, when mounted, might be designated as disk6s3s1 and disk6s3s2. Zero or more snapshots can be persistently defined on a volume, but only "active" (mounted) snapshots have disk identifiers.

It is important for software to avoid relying on numerical ordering of any of the parts. Activities including but not limited to partition deletions and insertions, partition resizing, virtual volume deletions and additions, device ejects and attachments due to media insertion cycles, plug cycles, authentication lock cycles or reboots, can all cause (temporary) gaps and non-increments in the numerical ordering of any of the parts. You must rely on more persistent means of identification, such as the various UUIDs.

Related Question