07-27-2012 05:23 AM
On SRX Series devices, the factory default for the maximum number of backup configurations allowed is 5. Therefore, you can have one active configuration and a maximum of five rollback configurations. Increasing this backup configuration number will result in increased memory usage on disk and increased commit time.
To modify the factory defaults, use the following commands:
root@host# set system max-configurations-on-flash number
root@host# set system max-configuration-rollbacks number
where max-configurations-on-flash indicates backup configurations to be stored in the configuration partition and max-configuration-rollbacks indicates the maximum number of backup configurations.
07-29-2012 10:04 AM
In Junos , by default , active configuration and first 3 rollbacks will be stored in /config directory and remaining rollback files (from 4 upto 49) will be stored in a different directory /var/db/config .
We can change these defaults ,with the following two statements ...
max-configurations-on-flash : refers to /config directory . For example, if you set a value of 2 here, active config plus first 2 rollbacks will be stored in /config.
 lab@srx3# show system max-configurations-on-flash max-configurations-on-flash 2  lab@srx3# run file list /config/ /config/: .snap/ hsconfigs/ juniper.conf.1.gz juniper.conf.2.gz juniper.conf.gz juniper.conf.md5* license-status.db usage.db
max-configuration-rollbacks : refers to the total no of rollback files to be stored. For example , if you set a value of 4 here, you can rollback upto 4 files. Out of these 4 rollbacks , 2 files (max-configurations-on-flash 2) will be stored in /config and remaining 2 will be stored in /var/db/config.
 lab@srx3# run file list /var/db/config/ /var/db/config/: hsconfigs/ juniper.conf.3.gz juniper.conf.4.gz  lab@srx3# rollback ? Possible completions: <[Enter]> Execute this command 0 2012-07-29 16:40:14 UTC by lab via cli 1 2012-07-29 16:39:35 UTC by lab via cli 2 2012-07-29 16:38:28 UTC by lab via cli 3 2012-07-29 16:37:31 UTC by lab via cli 4 2012-07-29 16:34:56 UTC by lab via cli | Pipe through a command 
Suppose , if we set both values to 4 , all rollback files (junper.conf.n.gz, where n=1,2,3,4) will be stored in /config itself, no files will be stored in /var/db/config.
Hope this helps !!