The cloud storage is secured using two independent methods.

Snapshots

Snapshots provide an easy way to reconstruct accidentally deleted, modified or damaged files or directories. Any user can find and restore older versions themselves (user-controlled recovery) without having to contact an administrator, service desk, etc.

How do snapshots work? The storage system automatically and regularly takes snapshots of all files and directories that exist in a file store at the time of the snapshot. Thus, snapshots are not a type of backup copy of every version of a file or directory that has ever existed, but only specific versions at defined points in time.

Snapshots created by the storage system can only be read (read only). However, files or directories restored from these snapshots can be edited again as normal. It should be noted that any open files at the time of the snapshot may be in an inconsistent state. Such restored files may be unusable. In this case, it is possible to revert to an earlier snapshot, for example.

The space used by snapshots on the file server is not counted against the quotas. However, in special cases (e.g., infrequent, very large changes to the entire dataset), snapshots may consume more disk space than is allocated for them. In this case, snapshots reduce the storage space on the file server.

A fixed number of snapshots is always kept: when a new snapshot is created, the file server automatically deletes the oldest snapshot of the same type and rotates the numbering of all other snapshots. There are three different types of snapshots, which are summarized in the following table.

Backup to magnetic tape (ISP backup)

Every night, all files are backed up to magnetic tape using ISP (IBM Spectrum Protect). These files can only be restored for the users upon a service request via the LRZ servicedesk. A maximum of three versions of a file are available. Deleted files are still available for 18 months.