mudele; the method you mentioned in your op and then relinked by the last poster is one of the most up-to-date methods to root the A855 (OG Droid). Rooting the phone in and of itself shouldn't result in the need for a backup to restore to; the A855 is pretty much un-brickable.
However, this other method:
[HACKS] Root Droid 1 - regardless of OS version
will offer for you exactly what you want, as in the first part it flashes a custom recovery (SPRecovery) which will allow you to make a backup of your phone before you actually apply through said custom recovery the file(s) that root it.
Read carefully and you will see what I mean.
That message is caused by this:E: Can't mount /dev/block/mmcblk0p1 (or /dev/block/mmcblk)
(No such file or directory)
E: Can't mount SDCARD:update.zip
Enable USB Mass Storage were showing under the mount options.
That message is caused by this:
And I got your PM this morning, I tend to go to bed pretty early. Unfortunately, by now, you'll probably have to start over, since I am sure you have booted your phone by now. This method will not work if you boot your phone normally after flashing the .sbf file. You must boot into SPRecovery first and apply that file as in steps 13-16 otherwise the custom recovery is overwritten. The file will fail if you still have stock recovery.
9. The SBF install goes fine, but when I go to apply the update.zip file in SPRecovery I get an error that it can't mount /sdcard (I can't reproduce -- need exact error message).
In SPRecovery, go into "mount options" from the main menu.
Ensure you see "Mount /sdcard". If you see "Umount /sdcard", your SD card is mounted -- choose "Umount /sdcard" to unmount it.
Ensure you see "Enable USB Mass Storage". If you see "Disable USB Mass Storage" your mass storage is enabled, choose "Disable USB Mass Storage" to disable it.
Then try to install the update.zip again.
10. The SBF install goes fine, but when I go to apply the update.zip file in SPRecovery I get this error:
E:Can't open /sdcard/update.zip
(No such file or directory)
Your update.zip file is not on your SD card or is named wrong. Read step #3 of the detailed procedure carefully. You've probably named the file update.zip.zip because Windows is configured to hide your file extensions.
which means exactly that. It does not say Ensure you have mounted /sdcard.Ensure you see "Mount /sdcard"
Well, I just don't know. There is something that you must be doing wrong, but without being there to look over your sholder I don't know what it is.
You have re-iterated the things in the thread that I pointed out about making sure your sdcard is not mounted and USB Mass Storage is turned off as that is what MC1 is saying.
which means exactly that. It does not say Ensure you have mounted /sdcard.
Try printing it out and carefully checking off the exact steps as you go.
Or you can find my sig and go to my "Root any Moto A855 guide". I have the manual method to install the root files etc., but it requires adb and is much more technical.