LAMP error: session_start() failed: No space left on device (28), but

Ubuntu server 10.04, Apache 2.2.14, PHP 5.3.2, MySQL. For the drive where session files are stored:

df -h:

Filesystem            Size  Used Avail Use% Mounted on
/dev/md1              450G   86G  341G  21% /

df -ih:

Filesystem            Inodes   IUsed   IFree IUse% Mounted on
/dev/md1                116M    9.4M    107M    9% /

Any ideas?

Answer

Finally remembered to answer with the solution! Turns out there were too many files in one directory. Had to start hashing the session files into subdirectories.