Pegasus2 R4 cannot be opened by Mac Studio M1 Ultra after initialization with Promise Utility.

  • Last Post 22 March 2023
Michael Scarbrough posted this 21 March 2023

Pegaus2 R4 has been functioning normally after upgrading firmware to 5.04.0000.64 on older iMac then connecting to my new Mac Studio M1 Ultra running OS Ventura 13.2.1. It is set up as a RAID5 drive which has not been changed since purchase with 4x 3TB Toshiba drives installed by Promise. I have Promise Utlity 4.06.0000.04 loaded onto the Mac for management.

After transferring desired files to the Mac Studio internal SSD, I performed a full initialization with Promise Utility to clear all data intending to use it for Time Machine back-up. After restarting my Mac, a warning pop-up appeared which presented an option to "initialize", which I did NOT perform again with Disk Utility. Pegasus does not mount and Disk Utility says it is "uninitialized". What steps must be performed for the Mac to mount it and retain the current logical drive? Why would an initialization with Promise Utility render it unreadable and mountable?

Thank you

Order By: Standard | Latest | Votes
R P posted this 21 March 2023

Hi Michael,

The CLI init is used to zero out the RAID. It will delete all data on the RAID including the filesystem.

When macOS sees a disk with no filesystem, it directs you to the Disk Utility to initialize and format the disk with HFS+ or APFS. You will have to put a filesystem on it before it can be used.


Michael Scarbrough posted this 21 March 2023

I stumbled upon the solution... I needed to format the logical disk after initialization. Not being a technical expert, it would have helped me if the manual indicated this would need to be performed after an initialization. I found this in the submenu under the Logical Drive "View" three dots icon for the Logical Drive listing the Format option. After this was done as Journaled HFS+, the Pegasus mounts correctly. Next, will try using it, but appears it should function normally now.


Michael Scarbrough posted this 21 March 2023

Thanks R P. I did not see your post until later, but found the solution. Good to know the background of what happened.


Thank you!

R P posted this 22 March 2023

Hi Michael,

If you use the Wizard it will create a RAID5 and put a filesystem on the RAID at the same time. It also names the LUN with the device type, example 'Pegasus3 R8'. You'd have a disk icon on the desktop in 1 or 2 minutes.