Slow write speed RAID 5

  • Last Post 08 December 2018
Samuel Wilkerson posted this 06 December 2018

Hello, I recently got a used Pegasus3 R6 and am getting slower write speeds than expected in RAID 5. Array is currently empty. Test using Crystal Disk Mark. Are these typical RAID 5 write speeds?

RAID 0: 1093 MB/s Read  927MB/s Write 

RAID 5:  935 MB/s Read   134MB/s Write

MOBO: Z370-AORUS-Gaming-7-rev-1 w/ Alpine Ridge Thunderbolt Card


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Pradeep Chidambaranath posted this 07 December 2018

Hi Samuel,

Kindly go to the KB link below to get the performance sepcifications for Pegasus3 units.

Kindly follow the steps below to enable forced read ahead.

How to enable controller forced read using Promise CLI:

1. Login using your Administrator and from a terminal in your Mac host type “promiseutil”

2. From our CLI type: ctrl -a mod -i 1 -s "forcedreadahead=enable"

If you still have any issues, kindly go to to create a support ticket with the latest subsystem report for further investigation.

Pradeep C

Samuel Wilkerson posted this 08 December 2018

Thanks for the info. I'm on windows tho, what would the comand line instructions be?



Samuel Wilkerson posted this 08 December 2018

I think I just figured it out. For windows: go to Device Manager. Right click on the array and choose Properties. In the Policies tab, choose Better Performance and check the box Enable write caching on the device.


Now getting about 900MB/s Read and Write in Raid 5.


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