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Of course we don't know exactly what you did after you logging into the NAS.  Normally you'd enter the following commands to get normal access to the OS partition:

# start_raid.sh
# mount /dev/hdc1 /sysroot
# mount --bind /proc /sysroot/proc
# mount --bind /dev /sysroot/dev
# mount --bind /dev/pts /sysroot/dev/pts
# chroot /sysroot /bin/bash

This assumes you are running XRAID. (Note you don't actually enter the # at the beginning).

After that you can look at the OS fullness by entering:

# df // -h
# df // -i

The first command tells you how much free space there is on the OS partition.   Normally only 25% of the space is used.

The second command tells you how many inodes are used.  It's rare to run out of inodes, but it can happen, so it's worth checking.