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To recover a file from tape, the tape first has to be mounted and searched for the file. As tape is a sequential media, this can take several minutes depending on the technology used. To recover a file from disk is only going to take as long as it takes to copy the data over the network to the destination disk. The search time is negligible.
The tape solution can be faster when recovering larger amounts of data as tape drives can deliver more data faster than disk drives. This premise holds true as long as all data is on one tape only and not spread out. If the recovery requires the restore of a full backup and several incremental backups, it may actually be beneficial to hold the incremental backups on disk and let the backup and restore system restore the full backup from tape and the incremental data from disk.
To reduce the recovery time even further, you can hold clone or snapshot copies of data on disk. A clone is a full copy of the data you want to restore, whereas a snapshot copy only holds changed data. Restoration can be instantaneous when using snapshot copies or clones because you only have to mount the copy on the application server, rather than the primary data volume, and no data has to be copied at all during restore.
HP uses the term “Business Copies” for these data snapshots. The easiest way to manage recovery from a Business Copy is to use HP Data Protector with the Instant Recovery option. This automatically detects and uses the Business Copy, and the administrator can use the standard HP Data Protector interface for instant recovery of applications.
The backup window can be reduced by taking a snapshot of the application data and moving it offhost for backup. The solution is called Zero Downtime Backup and uses either snapshots or clones of data in the disk arrays in combination with HP Data Protector.
The backup window can also be reduced by using backup to disk, running many backups in parallel. This is especially attractive for incremental backups because tape backups are fast as long as the tape drives are streaming, that is, enough data is being sent to the drive so it does not have to stop and then re-start when it receives more data. With the ever-increasing performance of new tape drives, the requirement on the infrastructure for backups is increasing, too—faster networks, faster disks, and faster backplanes. Especially when running incremental backups, many parallel streams are required to feed enough data to the drives. Even though less data is copied than for a full backup, the incremental backup can take longer to complete due to slow disks on the client side and nonstreaming drives.
To resolve that problem, backup to disk can be used as a staging area. All incremental backups are stored on disk and can then be written to tape later in one pass, without delay, as all the data is in one place.
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