E-Mail Inbox Mirror

E-Mail Inbox Mirror

The users' e-mail inboxes are now mirrored to our Network Appliance filer, and thus implement snapshots, allowing for finer-grained backups of incoming e-mail.


Inboxes associated with UNIX user accounts are mirrored (copied) several times a day to a directory on the NetworkAppliance Filer (where home directories and many project filesystems are stored). The volume to which the inboxes are mirrored receives periodic snapshots which maintain the contents of the files at those times.


Mirroring is a non-specific term for various methods of keeping a possibly real-time copy of data in another directory, volume, or server, etc. In this case, the granularity is several hours. Approximately five times a day (this number could change), inboxes are compared with the mirrored copy, and if the inbox is newer, it is copied to the mirror. This is an improvement over the previous one day granularity of inbox copies made as part of our departmental daily incremental backups.


A snapshot is accomplished via a mechanism which keeps track of blocks deleted from your files as they are changed or deleted. Thus the original file (at the snapshot time) can be instantly reconstructed from current and saved (via the snapshot) blocks. On the NetApp volume, several concurrent snapshots are kept track of, and old snapshots silently go away as new ones are created.

The mirror copies of inboxes get snapshots several times a day along with the rest of volume. The mirror times are timed to interleave with these snapshots.

Frequency and duration

Snapshots on this volume occur approximately five times per day. Four of these are hourly snapshots, and one is a nightly snapshot. The six most recent hourly snapshots are kept online, and the two most recent nightly snapshots are maintained. This allows for various times during the past two days that snapshots of an inbox are available. This is in addition to the copies available from incremental and full backups.

Access to the mirror and snapshots

The inbox mirror directory is /auto/mail.snap. Permissions are set such that an inbox mirror can only be accessed by its owner. The snapshot copies are in the .snapshot subdirectory of /auto/mail.snap. To see the times of your inbox snapshots, copy one of them (before it goes away), and view it with pine, run these (or equivalent) commands:

   % cd /auto/mail.snap
   % ls -lt .snapshot/*/biff 
   -rw-------  1 biff  mail    5581 Dec 23 06:58 .snapshot/hourly.0/biff 
   -rw-------  1 biff  mail    5581 Dec 23 06:58 .snapshot/hourly.1/biff 
   -rw-------  1 biff  mail    5581 Dec 23 06:58 biff 
   -rw-------  1 biff  mail    8396 Dec 23 03:01 .snapshot/hourly.2/biff 
   -rw-------  1 biff  mail    5344 Dec 22 21:51 .snapshot/nightly.0/biff 
   -rw-------  1 biff  mail       0 Dec 22 12:13 .snapshot/hourly.3/biff 
   -rw-------  1 biff  mail       0 Dec 22 12:13 .snapshot/hourly.4/biff 
   -rw-------  1 biff  mail   11098 Dec 22 04:09 .snapshot/hourly.5/biff 
   -rw-------  1 biff  mail    1557 Dec 21 19:42 .snapshot/nightly.1/biff 
   % cp .snapshot/hourly.5/biff ~/mail/inbox.save
   % pine -f inbox.save

Recovering from backups

Inboxes are also backed up as part of our departmental tape backups. If you need an instance of an inbox restored that precedes the online snapshots, please fill out the restore request form.

If you have any questions, please contact the Lab Staff.