Tips On Disk-to-Disk Backup, Part II

As I discussed in last month’s column, every organization should at least consider some sort of disk-to-disk backup solution.

Whether looking to increase backup and recovery speed or reliability, extend the useful life of existing tape or disk devices, or just looking at expanding a current backup solution, disk-to-disk backups are the way to go. Even a small amount of disk can make a dramatic difference to how the entire enterprise operates. And there is a solution for every budget and need.

There are essentially three ways to implement a disk-to-disk to tape backup: from the host, from the SAN (in the form of an appliance), or within a tape device.

This column will take a closer look at the host-based option.

Tech Talk

Typical backup solutions usually consist of three pieces: backup server, backup client and a tape device.

The backup server is usually a server that is dedicated to do nothing but backup other devices in the enterprise. It typically runs some sort of enterprise-class backup software (Veritas, Commvault, Legato, etc.) to backup its clients and manages one or more tape devices.

There may be more than one backup server in a backup solution, but there is typically a single “master” server to manage the other servers.

The backup clients are usually other servers in the enterprise (exchange servers, Oracle servers, etc.) that run a client version of the backup software and can’t afford to be bogged-down with the backup server tasks.

Most clients communicate to the backup server over a TCP/IP network and all their data flows over this network to the backup server which stores it on tape. There are also more advanced clients available that allow the client to act like a server and back itself up to its own tape devices or utilize shared tape devices attached to a SAN.

A tape device is a unit that contains one or more tape drives (typically LTO or DLT technology). A tape device can be a standalone drive that only holds one tape or a library system that holds multiple drives and tapes.

With a disk-to-disk backup solution, disks are added to replace or enhance an existing tape device. Most storage providers can sell some sort of large capacity, lower cost, storage solutions to fit into this space.

These devices usually provide some sort of RAID protection and can grow up to many dozens of tera bytes in capacity by using large-capacity SATA drives. In fact, for many storage vendors, the SATA solutions use the same core technology as their fiber-channel solutions.


Implementing a host-based disk-to-disk backup solution is typically very simple to do. Most of the major backup software providers can enable their disk-based backup solution with a software key or by adding a small upgrade to the existing backup server software.

Once the software is installed, it just needs to be configured so that backups will reside on a disk pool instead of a tape device. Backups can then be copied to tape for archival. The backup software will use the storage the same way it uses tape. Backups will still have backup retentions, etc.

Recoveries will come from disk instead of tape which will drastically reduce recovery times. The solution is completely transparent to the backup clients. The only difference the client will see is that backups and recoveries will almost always be faster. Backup administrators will have little or no learning curve.

Business Case

Justifying a host-based disk-to-disk backup solution is usually very easy to do. The software itself is usually relatively inexpensive and straightforward to implement. Large capacities of inexpensive SATA storage can be added to the solution very easily.

Budgets slated to replace, upgrade or add tape libraries can be used to purchase the SATA disk pool. Since the tape libraries will now be used to archive copies of the backups instead of being an integral part of the nightly backup process, support for the existing libraries can be dropped to very basic 8:00AM to 5:00PM, Monday through Friday or “time and materials” to further lower the TCO of the solution.

Using the disk pool for the most critical servers will free up the tape devices to be used to backup other servers faster or to backup servers that have been neglected in the past. Additional upgrades to the solution will consist of adding more SATA drives to an existing storage device.

Another part of a traditional tape library upgrade is to pay for the data on the old tapes to be migrated to new tapes. This can be costly and time consuming.

This step completely goes away since the old libraries are retained and the backup server will be able to track the tapes in the libraries until they age out of the system. The remaining tapes can now be used for archival purposes and will usually last longer than if they were used for day to day backups.

Jim McKinstry is senior systems engineer with Engenio Information Technologies, an OEM of storage solutions for IBM, TereData, Sun and others.