Snapshot backup
The general rules regarding backup of databar accounts are as follows:
- It is the responsibility of the users to keep backups of their own files.
- Databar Support maintain tape backups using the following backup schedule:
- Full backup twice a month, incremental on all other days.
- The retention period is one month.
- Once each semester, a full backup is given a retention period of two years.
- The purpose of the Databar Support operated tape backup is to protect user data in case of hardware failure, theft etc.
- Only in very special situations will Databar Support be able to assist individual users in recovering files from tape backup.
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Snapshots
It is now possible for users to recover files from snapshot backup without having to involve the Databar Support. A snapshot is a locally retained, point-in-time image of the file system. It provides users with very efficient and easy-to-use means of restoring old versions of their files - completely on their own.
Is this feature enabled for my account?
The snapshot technology is a feature of the central NAS appliances and so is only available here. But with only very few exceptions, all databar accounts have their home directory located on one of the central NAS servers and thus have the snapshot functionality enabled. You know you're on a central NAS file system, when the path begins with /xbar/nas1 or /xbar/nas2.
How do I access snapshots?
Every directory contains a special hidden ".snapshot" directory, which you can change to using "cd .snapshot". You have to know it's there though, since you can't see it, even with "ls -a".
The .snapshot directory contains multiple subdirectories named hourly.x, nightly.x and weekly.x. These contain old read-only images of the directory taken at different points in time. The exact point in time for each snapshot is equal to the access time of the directory as displayed by the "ls -lu" command.
You can use normal file system commands (e.g. "ls", "cd", "find", "cp") to find and copy your files back to the "live" file system.
How is the snapshot schedule?
Old snapshots automatically expire as new ones are generated. So you should act quickly, if you need data from a snapshot. The general schedule is:
- "hourly" snapshots taken every day at 4:00, 8:00, 9:00, 10:00, 11:00, 12:00, 13:00, 14:00, 15:00, 16:00, 17:00, 18:00, 19:00, 20:00
- nightly snapshots taken nightly at 0:00
- weekly snapshots taken Monday at 0:00
Except for the /xbar/nas1/hpc1 file system for HPC users. Due to excessive amounts of changes in this file system, snapshots tend to grow large, and so we've had to reduce their time to live. So the schedule for /xbar/nas1/hpc1 is:
- "hourly" snapshots taken every day at 8:00, 12:00, 16:00, 20:00
- nightly snapshots taken nightly at 0:00
However, we may occasionally have to delete one or more snapshots manually and without warning when the situation warrants this - e.g. when a file system has been filled up, and we need to free some disk space fast.