High Read and Low Write speed

  • Last Post 28 November 2019
TA Franks posted this 25 September 2019

Hi, maybe I can get some help regarding my dilemma. The Pegasus R8 RAID is acting kinda weird. It was originally set up using the Wizard  using the Express configruation as a Video Stream. But when noticing the RAID beeing slow during a copy process I ran a Speed test (AJA System Test)  with the following results:

1GB ProRes (HQ) = 24 MB/SEC Write - 715 MB/Sec Read

4GB ProRes (HQ) = 24 MB/SEC Write - 705 MB/Sec Read


Setup is macOS 10.14.6 Mac Pro Late 2013 connected directlty over Thunderbolt.

Configurate has RAID 5 using 7 Disks with one spare.


Thank you


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Raghuraman Kannan posted this 26 September 2019


Please check the Logical Drive Cache Policy and confirm if its in Write Back / Write Thru. For better performance, it has to be set to Write Back. 

If still not working , kindly register yourself as a user @ https://support.promise.com and open a new case with Subsystem Report.

Steps to save the subsystem report :


1) Open Promise Utility.

2) Click subsystem information icon on the top of the window.

3) Click the lock symbol on the left bottom corner of the screen to unlock the utility.

4) Click on save service report button to save the subsystem report and attach it to the case.

Thanks !

TA Franks posted this 27 September 2019

Its set to Write Thru when I change the settings to Write Back I get the result:

1GB ProRes (HQ) = 501 MB/SEC Write - 186 MB/Sec Read

4GB ProRes (HQ) = 494 MB/SEC Write - 657 MB/Sec Read


I dont have the option to set them to both.



Paul McDonald posted this 22 November 2019

I have been trying to work out my similar issue for a long while.

We have 3 identical systems with Pegasus R4 - 4x 2TB drives - Raid 0

2 systems were giving 700mb/s read and write speeds

my system was giving 400 write and around 700 read.

Logical cache policy was set to ReadAhead/WriteThru for all systems.

I changed mine to ReadAhead/WriteBack and it now has read/write speeds of 700mbs

so thanks for the suggestion... happy now...

Bit confused as to why??

any ideas?

Would the OS version on the main internal drive have anything to do with it?






Shafikur Rahman posted this 28 November 2019

Hi Paul,

 The OS version doesn't matter on the performance . The performance varies on the disk factors and the cache policy set.



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