How to Plan Your Disk-Based Backup with NAS or VTL - Understanding Your Requirements

Data growth is a fact of life for IT departments according to ExaGrid Systems CEO Bill Andrews. As your business grows, so does the amount of data it generates, and the amount of storage capacity needed to properly retain the data cascades out of control.

How to Plan Your Disk-Based Backup with NAS or VTL—Understanding Your Requirements Organizations of all sizes face the dilemma of how to backup increasing amounts of data while reducing the hassles of traditional tape-based systems.

In response, organizations are implementing new solutions using disks as the backup medium. The backup server copies the data to a disk-based system in the data center. This means that backups are faster, restores are more reliable and you will not have to deal with the hassles of tape management. Disk-based backup ensure better backup and restore performance and long-term data integrity, availability and security of your data. This makes disk-based backup one of the hottest topics in the data storage industry today.

When considering a disk-based backup system, there are many branches in the decision tree to consider when selecting the right solution for a given environment. Companies with 1TB to 100TB of data tend to set up disk-based backup as a NAS (network-attached storage) target. NAS is hard disk storage that is set up with its own network address rather than being attached to the department computer that is serving applications to a network's workstation users. The NAS device is attached to a local area network (typically, an Ethernet network) and assigned an IP address.

Those companies with more than 100TB of data, in a Fibre Channel environment, tend to set up disk-based backup with a VTL (virtual tape library) interface fronting the disk. Fibre Channel is especially suited for connecting computer servers to shared storage devices and for interconnecting storage controllers and drives.

To understand the differences between the NAS and VTL options, it's important to keep the following factors in mind:

Onsite Disk-based Backup—Short Term Retention

The first decision is how much retention you will put on disk at the primary backup location. If you plan to keep a week or two of retention onsite, on disk, then any standard disk will work. If you are keeping short retention onsite, then any standard backup storage solution will meet the requirement. The three most common options are:

  • SCSI or SAS (Serial Attached SCSI)-connected disk set up as a disk volume
  • Ethernet-connected NAS server with disk
  • Fibre Channel connection with VTL (virtual tape library) software fronting the storage

A VTL provides the benefits of disk storage in a system that emulates a tape library to existing backup software.

Onsite Disk-based Backup—Longer Term Retention

If you plan to keep four or more weeks of onsite retention, or years of offsite retention, then the quantity of standard disk becomes too hard to manage and too costly to afford. Therefore, data reduction techniques that only store unique data (i.e. do not store the redundant data) can retain larger amounts of backup history using a small fraction of the disk required when using standard disk.

In this case, you should consider a disk-based backup system with built-in data deduplication technologies. Data deduplication systems employ a data reduction technique that identifies common "chunks" of bytes among multiple data files, and only stores these chunks once. Using this method, you can store data in less disk space.

There are two interfaces to data deduplication systems and two types of data deduplication in the next level down the decision tree. The interfaces are NAS and VTL. The two data deduplication methods are byte-level data deduplication and block-level de-duplication.

Byte-level data deduplication compares one backup to another, and only stores the bytes that change from backup to backup. Block-level data deduplication breaks the backup job into 8KB blocks. The blocks are compared via their hashes to find duplicate blocks, and then only unique blocks are stored. Both methods achieve approximately the same data reduction.

To summarize, the options available for data deduplication in disk-based backup systems are:

  • NAS with byte-level data deduplication
  • VTL with byte level data deduplication
  • NAS with block-level data deduplication
  • VTL with block-level data deduplication

In selecting the best approach for your organization, decide if you prefer NAS or VTL. This is typically determined by the environment for storage. An Ethernet environment will choose NAS and a Fibre Channel environment will typically choose VTL.

The final branch is to decide which kind of NAS or VTL disk-based backup system with data deduplication is preferred. The key considerations in making this decision are the following:

  • How the system is supported, managed and deployed
  • The desired backup and restore performance of the system
  • How the system grows and scales
  • How the system can size to the environment
  • The cost of the system

By understanding your backup retention requirements, your current storage environment, the different approaches to data de-duplication, as well as the key considerations for evaluating disk-based backup systems, you will be able to make an informed decision and select the correct system to meet the data backup and recovery requirements of your environment.

Bill Andrews has more than 20 years experience in storage strategies and security, leading numerous teams in high-tech high-growth companies. Most recently, Bill was the vice president of Pedestal Software. Pedestal quickly became a leader in the security auditing space. Pedestal was acquired by Altiris, a public company. Bill also held senior positions at Live Vault, Microcom and Bitstream. Earlier in his career, Bill held a series of marketing and sales roles at Data General and Compugraphic. He is a graduate of Fitchburg State College and holds a BS degree in Industrial Technology.