by peaslaker » Thu Jan 27, 2011 5:19 pm
As the developer of UBIT, I haven't ever had my hands on a GoFlex Home. It is just through the experimentation of other forum users that we have worked out that the GoFlex Home can use all the elements of the GoFlex Net solution and work correctly.
The best approach for getting back to an original set up is to change the least amount possible and just to use spare space where it is available. Changing the bootloader is a tightly defined change, confined to the first 512KB of NAND memory. If you back that up, then it can be restored easily. Swapping back and forth isn't generally a good idea because once that first segment of NAND memory has gone bad that is it... the device is dead. So although this method is reliable, it is only reliable up to a point. I use this method to test new releases of UBIT to make sure they conform to the install instructions.
In my experience of attempting to chain boot original firmware, I have to say that it is an unreliable process at best. Chainloading U-Boot images works in some scenarios and doesn't work for others. It works for Dockstar but doesn't work for GoFlex Net. There are too many variables that you are not controlling. Bootloaders like to be the first things run on a machine and do not guarantee sensible behaviour when other bootloaders have been doing their thing first.
Lastly, and again with regard to the Pogoplug firmware on the GoFlex Net, there is no guarantee that the newer U-Boot images will be feeding the kernel the same startup environment as the patched, customised OE environment. i.e. just copying the boot command doesn't result in a successful boot. Unpicking all the changes that have gone on since kernel 2.6.18 isn't really a viable strategy so it can be a non-starter to try and get an up to date U-Boot to boot OE kernels.
The long and short of all of this is that flip-flopping between OE and modified firmware isn't sensible or easy. Being able to revert to OE firmware now and again, or if you want to sell the device in the original spec is generally possible and reliable.
By the sounds of it you have already ventured away from standard spec and don't have backups. Most backup instructions describe dumping all of /dev/mtd0, where usually we are only modifying the first 512KB. The most reliable method of restoring is to only reflash the first 512KB of NAND with the first 512KB of the backup rather than flashing the whole of mtd0 (on pogoplug devices, this breaks the checksum on the OE U-Boot environment and the machine won't boot).
The backup we want is the backup made without inclusion of out-of-block (OOB) data, made with the command:
$this->bbcode_second_pass_code('', 'nanddump -nof mtd0 /dev/mtd0')
To get the first 512K of the backup file:
$this->bbcode_second_pass_code('', '
dd if=mtd0 of=mtd0_512 bs=512K conv=sync count=1
')
would like to answer them I'd be extremely grateful.