external hd recognition mount unmount
 

1. have a 40 GB space challenged PC added 160 GB external
2. Sometimes I can boot and at these instances both drives are visible on BIOS at advanced.
3. When not able to boot with error grub loading error 21 I go to BIOS and External not visible. Unplug physically, re-plug BIOS advance sees both click f9 for load default, boot and back in.
Solutions please and thank you

Hi,

Not enough information to really assist you with your problems.

I would suggest the you look at 'How to Ask Questions the Smart Way'. You should understand that we are not sitting behind you therefore you must provide sufficient information to help diagnose your problem. Distribution, kernel and possibly what you have tried to solve the issue. Read the link I suggested!