When you delete a file system, it spends some time in the span's recycle bin before being recycled (permanently destroyed). As long as it is in the recycle bin, you can use filesystem-undelete to undelete it. To view the contents of the recycle bin, you can use span-list-recycle-bin.
After a period of time (about seven days, or sooner if space is needed by other file systems) the recycle bin is automatically recycled and you can no longer use the filesystem-undelete command to bring back a file system.
The filesystem-undelete command was introduced in release 12.0. Earlier releases do not maintain a recycle bin; therefore, if a file system was deleted under an earlier software release, you cannot upgrade to 12.0 and then use 'filesystem-undelete' to undelete it.
In release 12.1, after a file system has been deleted and the time in the recycling bin has passed, the freed chunks are moved to a vacated-chunks list (VC list), which is stored in Cod. The vacated chunks are reused when you create or expand other spans. Reuse of the chunks avoids premature exhaustion of space and prevents the back up of recycled file systems with real disk storage.
This command and the recycle bin are described more fully in the man pages. You can only use this command from the CLI.