Disk-Assisted Backup Whitepaper

2
Overview
Advancements in technology and price reductions have recently made it possible to use disk together
with tape to improve data protection. Some of the benefits that the technology promises are:
• Reduced recovery time
• Improved backup performance
• Increased success rate of backups completed
• No or reduced need for multiplexing of backups to tape
• Branch office backup consolidation
With shrinking backup windows and increasing amounts of data, users are adding more tape drives
and implementing faster backup network topologies, including storage area networks (SANs). But for
cost reasons, and in distributed environments, users cannot have every host on the SAN. Nor can they
implement a direct-attached tape device to every host. The administration and ongoing management
would be difficult and inefficient. In this type of environment, backup to disk can help. Backup to disk
is essentially the process of backing up data to a disk device rather than to tape. Backups are then
copied to tape for long-term storage and disaster recovery.
Combining disk and tape for backup is not necessarily a cheaper solution than using tape only, and
to completely stop running backups to tape may be a risk. In any case, it is well worth the time and
effort to investigate how using disk in addition to tape could potentially give you a better backup and
restore solution.
Reduced recovery time
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 will 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 software with the Instant Recovery option. This
automatically detects and uses the Business Copy, and the administrator can use the standard HP
Data Protector software interface for instant recovery of applications.
Improved backup performance
The backup window can be reduced to a minimum by taking a snapshot of the application data and
moving it off-host 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 software.