Unable to back up my database

Hello, I've been trying to back up a mysql database but everytime I do, I run into this exception:````
mysqldump: Got errno 28 on write

So I restarted the mysqld to see if that would fix it. I wasn't able to bring mysqld back online and got another error exception:````
/etc/init.d/mysql: ERROR: The partition with /var/lib/mysql is too full! ... failed!

I'm not able to run a mysql instance anymore cuz it's been stopped and unable to start again.

I checked the size of the said partition using the command 'df' and this is what comes back:

Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/xvda             20325244  19486656         0 100% /
tmpfs                   513420         0    513420   0% /lib/init/rw
udev                     10240       112     10128   2% /dev
tmpfs                   513420         0    513420   0% /dev/shm
overflow                  1024         0      1024   0% /tmp

the partition at /dev/xvda reports that it is full. Which is strange because the dashboard at linode.com only reports that I'm only using 42% of the storage space on this linode. Any idea why or how I can resolve this issue?

FYI: I'm on the 1024 plan, running 32bit Debian 6 squeeze with apache2 and mysql. I use this linode to host a joomla website and a ticketing/invoicing app.