Very large file system backup hangs "Writing to media" on Mac OS X clients. After transferring approximately 8-14TB the job's status shows "Writing to media" with 0 transfer rate in the job monitor.
On Mac OS X version 10.4 (Tiger) the default Shared Memory is set to approximately 4MB
On Mac OS X version 10.5 (Leopard) the default Shared Memory is set to approximately 10MB
The recommended Shared Memory for Netvault Processes to share is approximately 512MB as shown below
Modify the desired settings inside /etc/rc
sysctl -w kern.sysv.shmmax=536870912
sysctl -w kern.sysv.shmmin=1
sysctl -w kern.sysv.shmmni=128
sysctl -w kern.sysv.shmseg=32
sysctl -w kern.sysv.shmall=131072
Note the relationship between shmall and shmmax. shmall is the number of pages (4k in size). shmall x 4096 = shmmax.
If the Filesystem backup still hangs "writing to media" if resources allow, double the shared memory setting and the backup should complete normally.