Hello,
I have recently switched from xen virtualization to VMware, because of some stability issues. So I'm not very experianced with VMware.
Now I have one issue with USB passthrough to guest system. I have one guest Ubunutu system which needs to be connected to 2 serial to USB adapters. At the beginning everything works fine, but unfortunately after about a week it just looses one or both serial adapters, message in kernel log (guest) is not very informative, just disconnected an that's it.
I have tired to remove USB device in vSphere and attach it again, in most cases it helps but sometimes (like now) it is not possible to remove USB devices. vSphere doesn't complain about anything but if I open VM settings again there is still attached USB device.
And anyway it is not good idea to weekly maunally remove reattach USB passtrough devices.
On xen I have used "socat" utility to passthrough serial connection from host to guest via virtual network. Unfortunately on ESXi I cant find anything like that. Other possibility is to try netusb, but I never haven't tried it and anyway there is no such tool on ESXi.
I have two questions:
-) do someone have ideas how to get rid of this issue of loosing devices? what I need is guest to have 2 serial devices, it is not necessary to passthrough exactly USB device.
-) is there a way how to automate device attachment/removal from guest? I mean possibility to create some script wich can be executed weekly to remove and reattach my USB devices.
It is acceptable to disconnect and reconnect for a short time devices, for example on weekly bases, but not manually 
Thank you,
Cheers!