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POWER > Systems Management > High Availability

Your Business Continuity Strategy Should Focus on Recovery, Not Just Backups


Developing a plan for business continuity is one of the most important projects a systems administrator can have. The irony is that in a lot of cases, disaster recovery (DR) planning is placed at a lower priority than most everything else. Because of a lack of urgency, administrators often focus solely on the backup and not on the recovery. However, recovery should be your focus.

What’s Your MTD?

You can determine your business continuity needs in different ways. One metric that’s often used is the maximum tolerable downtime (MTD). This measurement determines the worst-case scenario for your servers to experience downtime. It’s not a goal to strive for, but it establishes an upper limit before business is critically impacted (and you could lose your job).

The goal you want to set is called the recovery time objective (RTO). It is the length of time you have to get systems back online to prevent hitting that upper limit. Reducing the RTO to the smallest time frame should be the goal of DR planning. One method organizations use to reduce downtime is to create backups of not only the data, but also the entire operating system. Having a full-system backup prevents the need to reinstall the OS and applications before restoring user data. This process is called bare-metal recovery (BMR).

Disk Images vs. File-Based Backups

When the idea of backing up the entire system came into practice, the first method used was creating a disk image, which entails making a block-level copy of the system disk to a tape or to a file. At first, this seemed like a great way to capture the entire system, but as is often the case, the focus was on the backup and little regard was given to the recovery process. At the time of recovery, disk images can introduce many problems, such as how to transfer the image back to a system with no operating system, changes in hardware or disk sizes and the challenge of multiple disks. To solve those issues, file-based system backup utilities were created, including mksysb (AIX*), Ignite (HP-UX) and Flash Archive (Solaris). With a file-based archive, you have the flexibility to recover the entire system to differently sized disks or different hardware. File-based backups also allow individual file restores rather than the all-or-nothing disk-image approach.

Virtualization and Snapshots

Storix recently conducted a survey of Linux*/UNIX* systems administrators, and more than 75 percent reported that their production systems will be virtualized by 2015. The most common forms of virtualization for these systems are VMware for Linux and the IBM PowerVM* solution for AIX and Linux on Power*.

Virtual machines (VMs) run off of virtual disks, which are large files made to look like disks to the operating system. This leads many administrators to ask, “Why create a backup of all of the files on the VM when I can just make a backup of the virtual disk that contains everything?” Since it’s not advisable to back up a disk file while running, a snapshot copy is created so the virtual disk files can be backed up in a consistent state. This process is typically called snapshot backups.

History has repeated itself when it comes to BMR techniques and many systems administrators have fallen back into the old trap of backing up everything without regard to how it will be restored. In theory, an organization should be able to copy the virtual disk images back to the virtual host and boot the VM. In practice, however, snapshots have reintroduced problems that were solved long ago by file-based backup solutions—mainly the flexibility to restore individual files, the capability to restore to differently sized disks and the capability to selectively back up just the operating system.

David Huffman is the president and CEO of Storix Inc.



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