Question: I have one **HP Proliant ML 115 G5** (AMD) with the latest BIOS (**07-06-2009**) and recently I've installed an USB disk.  

This is a common problem on old Proliant servers.  

When you plug the USB disk, BIOS boot order changes and tries to boot via USB.  

So, I'll change the BIOS settings and make the SATA disk the default boot device.  

The problem is, when I need to unplug the usb disk, and plug it again later.  

I can't be always changing the BIOS settings...  

How can one solve this for ever?!?!

Answer: 
The firmware release you're on is the final release for that model, as it was end-of-life in 2009. There won't be much assistance from HP on this.

You didn't describe the usage scenarios, but since this is a server, what is the problem with leaving the system on and reducing the frequency of reboots? The USB disk is an additional drive (and not the boot drive), so there's no harm in plugging it after the system has booted, right?

Edit: Apparent HP does not support permanent attachment of USB disks in the scenarios you're describing. There's [an interesting workaround here](http://pressf1.pcworld.co.nz/showthread.php?101301-USB-HDD-Booting-problem), but that's about it.
1. Log a case with HP support identifying it as a bug/feature request. If have a HP account manager discuss this with them.
2. Wait for an updated BIOS and apply it.

Good luck.