OpenZFS on OS X

i love Arq.

i use it successfully to backup numerous and diverse filesystems to Wasabi/AWS S3 and Backblaze B2. but i also like local backups, and i have attached a second pool to my workstation and created a dataset for my backups, but something weird is happening. Arq can be told to use APFS snapshots as a backup source which is attractive because it's more efficient.

apparently Arq will create an APFS snapshot in this scenario, but

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08-Jun-2023 13:00:05 CDT Backup activity started
08-Jun-2023 13:00:05 CDT Arq version 7.22
08-Jun-2023 13:00:05 CDT macOS 13.3
08-Jun-2023 13:00:05 CDT Storage location: iconUserData (Folder:/Volumes/succor/localbackup/iow/icon/iconUserData:/)
08-Jun-2023 13:00:05 CDT Backup plan: Back up to iconUserData (C788FF48-30E4-4CB4-AECB-665366F83D1C)
08-Jun-2023 13:00:05 CDT Dataless-files policy: Report cloud-only files as errors
08-Jun-2023 13:00:05 CDT Preventing computer sleep while backing up
08-Jun-2023 13:00:16 CDT Creating APFS snapshot for sleeper (/Volumes/sleeper)
08-Jun-2023 13:00:16 CDT Created APFS snapshot for sleeper (/Volumes/sleeper)
08-Jun-2023 13:00:17 CDT Creating APFS snapshot for ICON (/System/Volumes/Data)
08-Jun-2023 13:00:17 CDT Created APFS snapshot for ICON (/System/Volumes/Data)
08-Jun-2023 13:00:17 CDT /cascade/people/zemory/research/notes: No complete backup record found; rescanning all folders
08-Jun-2023 13:00:17 CDT /Users: No complete backup record found; rescanning all folders
08-Jun-2023 13:00:17 CDT /Volumes/sleeper: No complete backup record found; rescanning all folders
08-Jun-2023 13:00:17 CDT /cascade/people/zemory/research/notes/soumatou: No complete backup record found; rescanning all folders
08-Jun-2023 13:00:17 CDT /cascade/people/zemory/research: No complete backup record found; rescanning all folders
08-Jun-2023 13:00:17 CDT /cascade/people/zemory: No complete backup record found; rescanning all folders
08-Jun-2023 13:00:36 CDT Error: /cascade/people/zemory/research/Locnot ƒ/WILDING/infrared/Brand_(sorted)/PRIMARE/A30.ir: APFS snapshot was unmounted by another process
08-Jun-2023 13:00:36 CDT aborted because our APFS snapshot was unmounted by another process
08-Jun-2023 13:00:36 CDT Removing APFS snapshot for /Volumes/sleeper
08-Jun-2023 13:00:36 CDT Removed APFS snapshot for /Volumes/sleeper
08-Jun-2023 13:00:36 CDT Removing APFS snapshot for /System/Volumes/Data
08-Jun-2023 13:00:36 CDT Removed APFS snapshot for /System/Volumes/Data
08-Jun-2023 13:00:37 CDT Backup activity ended

`cascade` and `succor` are both openzfs zpools, cascade is 4 nvme drives in mirrored stripe (2x2) via thunderbolt and succor is mechanical mirror (1x1) via usb.

internal volumes `/` and apfs volume `/µ` are APFS internal flash on the workstation.

the target of the backup is not using any flags for impersonation:

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succor/localbackup/iow/icon/iconUserData  com.apple.browse       on                                                 default
succor/localbackup/iow/icon/iconUserData  com.apple.ignoreowner  off                                                default
succor/localbackup/iow/icon/iconUserData  com.apple.mimic        off                                                default
succor/localbackup/iow/icon/iconUserData  com.apple.devdisk      poolonly                                           default

and the zfs datasets i'm trying to backup in this case aren't using impersonation either:

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cascade/people/zemory/research  com.apple.browse       on                               default
cascade/people/zemory/research  com.apple.ignoreowner  off                              default
cascade/people/zemory/research  com.apple.mimic        off                              default
cascade/people/zemory/research  com.apple.devdisk      poolonly                         default

cascade/people/zemory  com.apple.browse       on                        default
cascade/people/zemory  com.apple.ignoreowner  off                       default
cascade/people/zemory  com.apple.mimic        off                       default
cascade/people/zemory  com.apple.devdisk      poolonly                  default

`sleeper` is a USB attached SATA SSD and APFS volume.

Arq thinks that it is making an APFS snapshot of the `research` and or `zemory` datasets? Arq support provided:

> I don't understand. Arq checks the filesystem; if it's "apfs", it creates an APFS snapshot.
> So, for some reason, macOS is saying your filesystem is APFS.

i disabled the "use APFS snapshots" option and it's attempting another backup now. but if anyone has seen this behavior before and figured out what was happening i would love to hear about it.

i _do_ have some zfs datasets that are configured to present as APFS but they aren't in the backup plan above.

i created a dataset to be used by the iCloud Content Cache service i enabled on that workstation (and i love it, usually!) and it's been working great.

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% zfs get -r com.apple.mimic cascade | grep -nv - | grep -nv off
1:1:NAME                                                     PROPERTY         VALUE                SOURCE
12:36:cascade/it/cachefs                                       com.apple.mimic  hfs                  local
13:37:cascade/it/deviceManagement                              com.apple.mimic  apfs                 local


so no mimicry is happening in the posix paths i am backing up and there are no mimic attributes on the target destination pool at all.