HDD and Flash stick issues

Hi
I have issues where the storage, be it SATA HDD or USB flash just disappear
I mount, makdir, chmod and all is good, run crossepg to use usb/hdd for download but then when it completes, the storage device is no longer selected (back to internal) and on checking FS can no longer see device (though if you go to harddisk settings you can still initialise it)
have tried numerous Firmware and it happens on all of them, currently on openpli
has anybody managed to solve this ?