[j-nsp] snapshot problem with just hard drive config

[LOM]

Hi folks,
 
I have a snapshot problem.
I have a M7i with an only disk drive , there is no flash card.
 
When I request a system snapshot it says : 
----
rasmus at edi> request system snapshot 
Snapshot requires two pieces of storage media.
error: This is a hard disk only configuration, snapshot not supported.
-----
 
I know that snapshot is just copying "/" to "altroot/ and also "/config"
"/altconfig" , am I wrong ?
 
Why it need 2 pieces of storage media? Is there a way that I can get
snapshot ?

 
Do you have an idea,
 
thanks for all,
 
PS : show system storage output : 
 
 
 
 
rasmus at edi> show system storage 
Filesystem        512-blocks       Used      Avail Capacity Mounted on
/dev/ad1s1a           437522      64274     338248     16%  /
devfs                     32         32          0    100%  /dev/
/dev/vn0               21900      21900          0    100%
/packages/mnt/jbase
/dev/vn1               68408      68408          0    100%
/packages/mnt/jkernel-6.2R1.5
/dev/vn2               17680      17680          0    100%
/packages/mnt/jpfe-M7i-6.2R1.5
/dev/vn3                4108       4108          0    100%
/packages/mnt/jdocs-6.2R1.5
/dev/vn4               26888      26888          0    100%
/packages/mnt/jroute-6.2R1.5
/dev/vn5                9432       9432          0    100%
/packages/mnt/jcrypto-6.2R1.5
mfs:153              1016286          6     934978      0%  /tmp
/dev/ad1s1e            48570         50      44636      0%  /config
procfs                     8          8          0    100%  /proc
/dev/ad1s1f         36364494     811950   32643386      2%  /var
 
rasmus at edi>