iMac Intel 27" Retina 5K Display (Late 2014 & 2015)

Model A1419 / EMC 2806 / Late 2014 or Mid 2015. 3.3 or 3.5 GHz Core i5 or 4.0 GHz Core i7 (ID iMac15,1); EMC 2834 late 2015 / 3.3 or 3.5 GHz Core i5 or 4.0 GHz Core i7 (iMac17,1) All with Retina 5K displays

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Matt @matt1900

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crwdns2931729:0crwdne2931729:0: Mha 5, 2021

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Why my iMac show up this icon when turn on?

my imc 27” mid2015 core i5 show up this icon after i reinstall big sur on my new owc ssd. Does anyone know why? And will it reduce the speed of the ssd?