Space Issue Preventing New Attachments/causing error

[smooth-c]

Okay guys, around lunchtime yesterday my site started going a bit slow and I noticed trying to upload attachments gave this error;



Now, I thought this was a little strange so I rebooted my server and the issue went - a little while later, it came back so I tried logging into phpmyadmin and I see this error (which prevents me from logging in)

Warning: Unknown: write failed: No space left on device (28) in Unknown on line 0

Warning: Unknown: Failed to write session data (files). Please verify that the current setting of session.save_path is correct (/var/lib/php/session) in Unknown on line 0

I went to this directory and noticed there was lots temp files, so with the advice from another forum I deleted them. The issue seemed to resolve itself and then later on, it just started again so im here now.

Can anyone give me advice? this issue is driving me crazy and I really need to rectify it asap.

Many thanks,

Greg