Disk to Disk Backup (D2D)

Disk to disk backup is replacing the tape backup as a solution for short-term data retention. Disk storage costs decreased while the capacity of disk drives, especially SATA disks, increased, thus making disk a more attractive backup target.

Disk to disk backup has the benefit of faster backups and restores, occurring at disk speed. The backups are done on the disk staging area, where they are kept short-term. In the case of disk to disk backup, short-term retention has different meanings, depending on the corporate Data Retention policies. It might mean for example as long as 12 weeks, but at a minimum, probably will not be less than 1 month.

The target of a disk to disk backup can be conventional, RAID based, disk arrays, or a Virtual Tape Library, a disk device emulating a tape library. Using the RAID arrays you overcome the drawbacks inherently associated with tape backup. Disk access is random-access, not sequential access as with tape, so it can send and receive multiple concurrent streams.

However, the problem with conventional disks is the Total Cost of Ownership (TCO). Adding more disks is unavoidable, as the size of the backup data grows. To protect against data loss, you might also need to create duplicate backup sets through replication. Keeping all the backups on the disk staging area for the required periods of time is going to require a lot of disk space. Due to the high TCO of the conventional RAID based disks arrays, adding more disks might not be an option.

Here is where Data Deduplication comes to the rescue. Disk to disk backups can be done to a device able to deduplicate data based on policies. Such a device is a virtual tape library.

Conventional Disk to Disk Backup:

Disk to Disk Backup with Data Deduplication:

Disk to Disk backup can be part of different architectures:

D2D2D Architecture

In a D2D2D architecture, data residing on the staging disk area can be replicated through SAN-specific snapshot technologies to a remote backup disk system. From the remote disk, data can be sent to tape for long-term storage. This will substantially cut costs, as it results in smaller disk staging storage, which consequently requires a smaller replication target storage.

We need to emphasise here that, when talking about the replication process, we refer to replicating backups, not live data. Although data can be protected through mirroring and data replication, this type of protection does not constitute a “backup”, as it does not protect against data loss or corruption. If a file gets deleted, the “mirror” will reflect that almost instantly!

D2D2T Architecture

In a D2D2T architecture, data stored on the staging area will eventually be sent to tape, for long-term storage (archiving).