Issue storage pool

Question

Hi,
i'am new in this forum and i don't have enough expertise in the domain of storage Pool i have an issue since last week with my server
i have created a storage pool from Windows servers 2019 with 8 nas behind it and every nas have 4 disks so all the disks are healthy and fine
so the server is connected to the nas via Iscsci to the disks the virtual disk was working fine since last year and since last week suddenly
one of the nas appeared with yellow triangle i thought that it was the connection via Iscsci that was not done after checking i saw that the isci was ok but the triangle didn't disappear even after a repair of the VD now my backup system don't want to start because of that VD is not healthy
but the VD is accessible with the Data inside still and i have tried to retire one nas because the disks are not visible and i couldn't find the way to figure out witch disk is causing the issues knowing that all the disks in the Nas are ok and healthy