Drastic Difference in Speed of Two Identical Pegasus 2 R6 Raid Systems

  • Last Post 19 August 2020
Thomas Wheeler posted this 24 December 2019

I have two identical Pegasus 2 R6 raid 5 systems attached directly to the new 2019 Mac Pro through a thunderbolt 3 cable with an Apple thunderbolt 3 to thunderbolt 2 adapter on both systems at the point of attachment to the Mac Pro thunderbolt 3 ports.  Both of these Pegasus 2 systems have the same and latest firmware.  Both are connected with thunderbolt cables supplied by Promise with the systems. I am using Mac OS Catalina with the latest udates and I am using the Mac OS Catalina compatible (latest) Promise Utility.  Both of these Pegasus 2 R6 systems show a full green board in the Promise Utility. Both Pegasus 2 systems read and write fine, and I am experiening no disconnections or other problems.  However , in the Black Magic Disk Speed test one of the Pegasus 2 R6 systems shows an excellent read/write valuse of roughly 800 and 700 MB/sec while the other Pegasus 2 R6 system shows a write speed of only about 150 Mb/sec and a read speed of about 500 MB/sec.  

I am at a loss as to why there is such a vast difference in the write speed of these two identical Pegasus 2 systems.  Both have only about 2TB out of their totoal 15 TB capacity so disk space is not an issue. 

I would be most appreciative if anyone can tell me how to improve the write speed of the slower of these two Pegasus 2 R6 systems or explain what is likely going on here.  Thank you in advance for responding. 


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Ranjith kumar posted this 25 December 2019

Hi Thomas,

It may be issue with drive of the Pegasus2 which have low performance, but to confirm it, we need subsystem report. So kindly create a web support case at support.promise.com and attach the report in that case id.

Steps to save the subsystem report:

- Open promise utility
- Click subsystem information icon on the top of the Promise Utility window
- Click the lock symbol on the left bottom corner of the screen to unlock the utility
- Click on save service report button to save the subsystem report.

Below is the Promise KB link to know how to attach files to the web support case:



Promise Team

Thomas Wheeler posted this 25 December 2019

Thank you. I am preparing the web support case and the susbsysem report. 


M Wilson posted this 16 July 2020

Were you able to resolve the read/write performance issue from last December? I'm having a similar issue. Thx.

Ranjith kumar posted this 17 July 2020

Hi Wilson,

Kindly reach us through support.promise.com with subsystem report to help you on performance issue.


Promise Team

Smith Jones posted this 07 August 2020

The substitution drive ought to be of a similar limit and speed as the old drive.

Tommy Shelby posted this 19 August 2020

The substitution drive ought to be of a similar limit and speed as the old drive.

yeah i agree that must be the reason