/sys is the sysfs, it is not a real filesystem that is part of your hard drive/partition. From the top of the sysfs.txt documentation:
sysfs - _The_ filesystem for exporting kernel objects.
Patrick Mochel <email@example.com>
10 January 2003
What it is:
sysfs is a ram-based filesystem initially based on ramfs. It provides
a means to export kernel data structures, their attributes, and the
linkages between them to userspace.
In short, you don't need to back up /sys or /proc as they are dynamically updated by the kernel, don't physically exist on the hard drive, and any 'files' from them could not be restored anyway. You might want to look into using the "find" command with the "-prune" option in combination with "tar" to select the files/directories to backup... (you probably want to exclude /dev as well, IMHO).