Backup/Restore

If a file is lost from your account (e.g., if you accidentally removed a file you need), the file can usually be restored, since filesystem snapshots are done on a regular basis for most user-accessible filesystems unless requested otherwise. If you lose a file from your home directory or project space, it can usually be recovered by looking in the snapshot tree. If, however, your file was lost from a filesystem on which snapshots have been disabled, or if it is not in the snapshot tree for some reason, it is likely not possible to recover. Fill out the "Restore Files" form in the box to the left and we will investigate. Please specify the name of the file, including the path name of the subdirectory it was in, the date the file was most recently modified, and the date it was lost.  Due to the nature of the disaster-recovery tape-based backups (they are designed for recovering our entire storage system in the event of catastrophic hardware failure), and cannot reasonably be used for restoring individual files.  Snapshots should be consider your only form of backups. 

If you need help understanding this policy, please e-mail csstaff@cs.princeton.edu for clarification.

Backup Schedule (effective: 2020/06/15)

The following backup schedule is currently in effect for the CS Department. Backup dates and times are unspecified and are effectively random.

  • For all Home Directories:
    • User-accessible snapshots lasting up to 1 year.
    • Bi-weekly offsite DR backups with a retention period of 30 days.
  • For Project Filesystems:
    • (Optional) User-accessible snapshots lasting 30 days, 90 days, or up to 1 year, as requested.
    • Bi-weekly offsite DR backups with a retention period of 30 days.

Backups more than one year old are not available.

Snapshots

Home Directories and Project Space are both stored on filesystems that support snapshots. Snapshots are taken every four hours, and deleted on a regular basis such that there are generally several snapshots available from various times going back as far as one year. The snapshot retention timeframe, or the lack of snapshots, can be chosen at the time a project space is created, but cannot be changed for an existing space. If a change is required, a new space will need to be requested with the required parameters and data shifted, by the data owner, from the original space to the new.

In order to recover a lost file from the snapshot tree, cd into the directory from which you lost the file, and then into the '.snapshot' directory within that directory. You will not see the .snapshot directory in the output of 'ls', but if you are using a central CS filesystem (and have not requested to prevent it), it will be there. Below is an example of recovering a file called 'file' from the 'code' directory in the 'myproject' filesystem:


    cycles$ cd /n/fs/myproject/code
    cycles$ cd .snapshot
    cycles$ pwd
    /n/fs/myproject/code/.snapshot
    tux$ ls
    20111201-00:30-MONTHLY-PROJ/    20120216-00:00-NIGHTLY-PROJ/
    20120101-00:30-MONTHLY-PROJ/    20120216-12:00-Q4H-PROJ/
    20120130-00:00-WEEKLY-PROJ/     20120216-16:00-Q4H-PROJ/
    20120201-00:30-MONTHLY-PROJ/    20120216-20:00-Q4H-PROJ/
    20120201-01:00-QUARTERLY-PROJ/  20120217-00:00-NIGHTLY-PROJ/
    20120206-00:00-WEEKLY-PROJ/     20120217-04:00-Q4H-PROJ/
    20120213-00:00-WEEKLY-PROJ/     20120217-08:00-Q4H-PROJ/
    20120215-00:00-NIGHTLY-PROJ/
    cycles$ cd 20120217-04:00-Q4H-PROJ
    cycles$ pwd
    /n/fs/myproject/code/.snapshot/20120217-04:00-Q4H-PROJ
    cycles$ cp -p file /n/fs/myproject/code