DaVinci 18 + Mac Studio: low read speed from external disk

Sytem:
Mac Studio M1 Ultra, 20-core CPU, 64-core GPU, Memory 128GB, Monterey 12.5.1

Software:
DaVinci Resolve Studio 18.0.4 BUILD 5

Source Footage and disk:
Sony Venice X-OCN ST 4K UHD
Stored in a 12TB G-Drive connected via Thunderbolt 3 directly to the Mac Studio (4.4TB Free space)
≈480MB/s Write / ≈480MB/s Read (according to BM Speed Test)

Target Codec and disk:
MXF OP-Aton DNxHR LB HD 1920x1080 (No correction made only Burn-in)
Internal Mac Studio (3.55TB Free Space)
≈7000MB/s Write / ≈5600MB/s Read (according to BM Speed Test)

Issue and tests done:
When rendering from the G-Drive the disk read speed never exceeds ≈180MB/s, resulting in a 50fps rendering speed and GPU is a 1/3 of capability:



I tried copying a file from the G-drive to the internal drive and the read speed is around 485MB/s which corresponds with BM Speed test result:


Here is a picture of G-Drive read speed, note the spike is from the test done with BM Speed Test, then the steady low read speed when rendering:


I tried rendering the same file and same settings from the internal drive to the internal drive and it maximizes the GPU resulting in 222fps render

Question
Why the read speed from the external drive is so slow when rendering?

I have seen similar behavior with my Studio Ultra. A solution that works for me is keeping the original footage on. Raid 0 usb external drive, the Resolve project on by Studio boot SSD, and the output file directed to a 1 TB SSD external usb drive. 4K footage output to ProRes, input videos 4K h264, ProRes and mixed others. Output shows in excess of 200 fps.

Yes, I see what you mean, I also experience how fast the render can go rendering from internal to internal, it goes up to 222fps. In this case the footage ended up being more than my 6TB RAID0.
But I still don't understand why it does not take all the bandwidth of the drive's read speed, it does not make sense to me.

An Intel machine may behave quite differently, David.

I have no problems playing ArriRAW with 35 MB per frame from a NVme in an Acasis enclosure, so it's not the Mac or the ports.

When rendering from the G-Drive the disk read speed never exceeds ≈180MB/s, resulting in a 50fps rendering speed and GPU is a 1/3 of capability...

Gee, to me 50fps is fast, but it depends on how much correction and processing you're throwing at it. What happens if you replace the G-Drive with an SSD? How is the G-Drive formatted? How is the source drive formatted? Are all the connections TB3? DNxHR LB is not that hard a task, though it does take a little time to process from 4K (or 6K) to HD. Does removing the burn-in change the render speed?

By an amazing coincidence, we have the exact same build as you do for the Mac Studio, only we're running Monterey OSX 12.6 (which should not be that much of a difference). We're holding back on moving over to Ventura OSX until next year.

After more tests I can confirm the bottleneck being the disk itself.
There was no grade applied to the clips, just the Burn-ins, and the render was the same speed without them.
Trying different TB3 ports but same result.
Copied the file to an external SSD (≈380MB/s Read & Write) and it maxed the reading speed.
Still no idea why this could be happening.

FYI
G-RAID 2 from SanDisk Professional 12TB (2 HDD in RAID0) will not read to more than ≈180MB/s while rendering.

Did anyone ever figure out a solution to this problem?

I am running multiple base MAX Mac Studios, I have them connected to ARECA 8050T3U 8 bay RAIDS of various capacities. All in RAID 5. I am having the exact same issue as described here. If I render from the internal drive or an SSD (Sabrent 8TB) I get 370fps transcoding from UHD PRORES 4444XQ to DNXHD36 1080p, but reading from the RAID I am only getting 50fps.

These setups are being used by DIT's on set, so using other drives is not an option. It really makes no sense to me that Resolve can't use the full bandwidth (1700MB/s) of the RAID.

Any help would be greatly appreciated. Thank you.