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I have an OSX Sierra VM and I installed on a unassigned device with raw .img and Im having VERY slow write speeds.

I start the disk speed test and the speeds are great like 500mb/s but in seconds it drops to 80mb/s and 60mb/s and going down until get read at 8mb/s and writes at 6.2mb/s.

I already tried to chance cache from writeback to none and unsafe and native IO the start perfomance is the best with io='native'  on the disk but it get slow after during the test.

Edited by ulisses1478
fixed the problem an d posted the solution
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I'm having the exact same issue. 


Except i am passing the SSD through and not using an image. ( Prim vdisk location --- Manual - /dev/drive/by-id/ata-ct480bx500etcetc)


Mine starts fast at 100MB/s then drops after 10 seconds to 80MB/s then 40MB/s then to 0MB/s Then back up again for 4 seconds then drops back down until the file finished. 


By accident (didn't realise i could do this) booted into the drive bypassing unraid.  Did the same test and same thing happened. Tried different Sata slots, Cables, Different drives (both same model Crucial BX500) 


I plan on Installing windows directly to the drive to see if i experience the same issue. 


If i do i would assume there just horrible drives or its a compatibility issue with the motherboard. Where i will try a different computer.


anyway i will let you know the outcome. 

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18 hours ago, ulisses1478 said:

I have no problem with any os on the SSD im using it's just on virtual machine

Ok, well i am happy to say i have sorted my issue out. Just in case anyone ever has this issue something for them to try. 


I download Crucial SSD software originally to check and see if there was a new firmware (which there wasn't) so i saw it had a sanitize option (which wipes the drive completely) i don't know what made me want to do it, but i did it and its working 100% .. Sits on 98-113 MB/s 

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