Hi,
On my Mac Studio, Finder needs 5–6 minutes to show a folder of 14,400 image files on my RAID. A plain directory listing of the same folder takes 0.2 seconds, and Forklift and DaVinci Resolve show it almost instantly. Open/Save dialogs in every app have the same problem. I’ve had this for several years and several macOS versions.
Setup
- Mac Studio M2 Ultra, 128 GB, macOS 27.2 (also on 26.7.1 and earlier)
- G-Technology G-SPEED Shuttle XL, Thunderbolt 3 (Promise-built, PCI 105a:8870, PromiseSTEX)
- Pegasus DEXT driver
com.promise.driverkit.pegasus21.1.0, the only third-party driver loaded - Volume: Mac OS Extended (Journaled), 42 TB
Measurements
| Test | Files | Time |
|---|---|---|
| Plain directory listing, RAID | 14,400 | 0.21 s |
| Finder, RAID | 14,400 | 311–363 s |
| Finder, internal SSD | 5,000 | 0.3 s |
| Finder, HFS+ disk image | 5,000 | 1.5 s |
What I found
A sample of Finder shows that for each file it adds, Finder calls TFSVolumeInfo::AddVolume → TCFURLInfo::SamePhysicalDevice → _mountedVolumeURLsWithPhysicalDisksMatchingVolumeAtURL, which queries DiskArbitration (DASessionCreate / DADiskCopyDescription). During one test, diskarbitrationd used 3–4 minutes of CPU, but the Pegasus driver used only 1.5 s. On other volumes, Finder doesn’t repeat this lookup.
The one difference I can find is in how the volume appears in the I/O registry. The driver attaches the IOMedia objects (@0:0, @0:1, @0:2) directly under pci105a,8870@0 in the IODeviceTree plane. As a result, DiskArbitration reports this media path:
IODeviceTree:/arm-io/apciec1@30000000/pcic1-bridge@0/pci-bridge@0/pci-bridge@1/pci105a,8870@0/@0:2
Volumes on Apple’s own storage drivers get a full IOService path through the block-storage, media and partition layers instead. My guess is that this stops Finder from caching the volume’s physical-disk mapping, so it repeats the lookup for every file.
Questions
- Is attaching IOMedia in the IODeviceTree plane intended, and could the driver publish media only in the IOService plane?
- Is there a newer driver or firmware that changes this?
- Can you reproduce it with a folder of 10,000+ files on a Pegasus3 on Apple silicon?
Other users report the same symptom here, including one with a G-Speed Promise RAID on a Mac Studio M2 Ultra: https://forums.macrumors.com/threads/finder-slow-to-show-large-folder-contents-loading.2386040/
I can send the full Finder sample traces and a detailed PDF report.
Thanks!
