Mac: MacBook Pro 16-inch (Intel, 2019) macOS: Tahoe 26.5.1
I'm trying to determine whether this is expected behavior or a bug.
Setup
I purchased a new 2TB SSD to use exclusively for Time Machine.
Before configuring Time Machine, I manually erased the SSD in Disk Utility and formatted it as:
APFS (non-case-sensitive) Encrypted
I specifically did not choose APFS (Case-sensitive).
What happened
After selecting the SSD as a Time Machine destination and allowing macOS to prepare the disk, I later checked the volume information and found:
File System Personality: Case-sensitive APFS
and:
APFS Volume Disk (Role): Backup Name: Brad Mac Backups SSD (Case-sensitive)
The volume appears to have been converted to a dedicated APFS Backup volume and is now reported as case-sensitive.
Additional observations
After backups complete:
tmutil status
reports:
Running = 0
indicating Time Machine is no longer running.
However, Spotlight processes (mds and mds_store) continue accessing the backup volume for many hours afterwards, preventing normal ejection of the SSD.
Using:
sudo lsof | grep "/Volumes/Brad Mac Backups SSD"
shows Spotlight processes holding the drive open.
Finder's "Force Eject" works successfully.
Questions
-
Is it expected behavior in macOS Tahoe for Time Machine to create a Case-sensitive APFS Backup volume, even when the destination was originally formatted as standard APFS?
-
Has anyone else observed a Time Machine destination changing from APFS (non-case-sensitive) to APFS (Case-sensitive) during setup?
-
Could the case-sensitive APFS format be related to Spotlight continuously indexing the backup volume and preventing normal ejection?
Relevant Output diskutil info disk3s2
returns:
File System Personality: Case-sensitive APFS
and:
diskutil apfs list
shows:
APFS Volume Disk (Role): Backup Name: Brad Mac Backups SSD (Case-sensitive) Mount Point: /Volumes/Brad Mac Backups SSD 1
Any insight would be appreciated, as Apple Support was unable to explain why the backup volume became case-sensitive.