This article indicates that for MX routers that use the Junos Subscriber Management (JSM) feature, if filesystem /var of the Routing Engine has insufficient disk space, unexpected behavior can be seen. The article recommends that 5G or more space be kept available for the /var directory to avoid such problems.

For MX routers that are using the Junos Subscriber Management (JSM) feature, if filesystem /var of the Routing Engine has insufficient disk space, unexpected behavior can be seen.

It is recommended that 5G or more space be kept available for this /var directory. Additionally, keeping 40% or more of the filesystem size as available is better. The command show system storage can be used to check the storage usage of /var :    

Note: Refer to show system storage for detailed explanation of the command outputs.

For example:

user@jtac-mx480-re0> show system storage 
member0:
--------------------------------------------------------------------------
Filesystem              Size       Used      Avail  Capacity   Mounted on
/dev/md0.uzip            21M        21M         0B      100%  /
devfs                   1.0K       1.0K         0B      100%  /dev
/dev/gpt/junos         10.0G       1.6G       7.6G       18%  /.mount
devfs                   1.0K       1.0K         0B      100%  /.mount/dev
/dev/md1.uzip            23M        23M         0B      100%  /.mount/packages/mnt/os-libs-10
/dev/md2.uzip            25M        25M         0B      100%  /.mount/packages/mnt/os-runtime
procfs                  4.0K       4.0K         0B      100%  /.mount/proc
/dev/gpt/config         446M       324K       410M        0%  /.mount/config
/dev/gpt/var             14G       7.7G       6.3G       55%  /.mount/var        <- 45% of the filesystem size is available (1-55%), so it's good.
tmpfs                    43G        24K        43G        0%  /.mount/tmp
/dev/md3.uzip           1.6M       1.6M         0B      100%  /.mount/packages/mnt/os-zoneinfo64-ac3b4110
/dev/md4.uzip            20M        20M         0B      100%  /.mount/packages/mnt/junos-net
/dev/md5.uzip            18M        18M         0B      100%  /.mount/packages/mnt/junos-libs
/dev/md6.uzip            18M        18M         0B      100%  /.mount/packages/mnt/os-libs-compat32-10
/dev/md7.uzip           538K       538K         0B      100%  /.mount/packages/mnt/os-compat32
/dev/md8.uzip           107M       107M         0B      100%  /.mount/packages/mnt/junos-libs-compat32

When the available storage of /var is low, refer to request system storage cleanup to clean up the storage.