Saving for a rainy day

As primary storage grows, it drives up backup requirements. Even though hard disk costs have been falling, tape is still the cheapest option for secondary storage

Tape cartridges are synonymous with data backup in the SMB space. The prime reason behind the popularity of tape-based backup is its tried and trusted nature.

Although tape technology is behind disk technology when it comes to speed of access and ease of storage, its price-performance (or rather cost-capacity) still beats that of the disk. Yet another factor favouring tape is psychological. It is difficult to displace the mindset favouring tape overnight.

Tape cartridges can go up to hundreds of GB. Access speeds in hundreds of Mbps are commonplace. With 2:1 compression (some formats even provide 2.5:1), tape emerges as the right large-scale backup option for an SMB.

Chaos bazaar

Confusion abounds when it comes to tape formats. The market is flooded with options, so choosing the right one can be a big problem at times. On capacities, options range from a few hundred megabytes and all the way up to terabytes (compressed).

Then comes the war of the formats. The formats in vogue include SDLT/DLT, LTO, Mammoth, AIT, DDS-4, VXA, SLR, QIC, and Travan (TR-6). These have their own strengths and weaknesses at varying price points.

To choose the right media, a buyer has to conduct a price-capacity-features analysis. It is important to have an accurate idea of your backup requirements while doing this exercise.

Trusted media

The typical tape drive consists of media head and drive mechanisms to record or read from a cartridge. These come with SCSI or IDE interfaces to permit connectivity to servers and PCs.

A single drive and multiple cartridges along with backup software will suffice for a very small business. Tape drives are available in all the formats listed above.

Automating backup

Auto-loaders are meant for situations where a tape drive doesn’t cut it. An auto-loader is the robotic equivalent of an operator for taking tape backups. A typical arrangement consists of a tape drive, a robot arm to load and replace tape cartridges, and slots to hold the cartridges when they are not in use. As soon as a cartridge is full, the auto-loader replaces it with a fresh one.

A typical auto-loader may be able to hold anything from four to over 20 cartridges. They come with options of slot- or magazine-loading cartridges. Magazine-loading is useful if your requirement is for an unattended backup. Auto-loaders are usually controlled by backup software for better results.

Aggregating reels

If auto-loaders were at lower and mid-levels of automated tape backup, tape libraries are at the highest point of the automation curve. These are required only for backup requirements of medium businesses or large enterprises.

Tape libraries consist of multiple tape drives, robotics, and cartridge slots for backing up huge quantities of data. A big advantage of using a tape library is that it is possible to have tape drives of different formats within the same unit. This is useful for daily backup size requirements that vary dramatically. With compliance requirements growing, these devices are going to be in demand with medium businesses.

The typical tape library comes with an SCSI or Fibre Channel interface. Apart from the larger medium businesses, most SMBs are unlikely to opt for a tape library.

Simulating tape

One of the biggest problem with tape is that tape-based backup devices cannot keep up with the throughput of a server or a storage array or NAS box. Virtual tape servers came about as a solution to this problem. These are hard-disk-based devices that simulate the functioning of a tape library by acting like a ‘buffer zone’ between the faster primary devices and the slower tape backup. To the servers and primary storage, they ‘look’ like a tape library. However, they can accept vastly higher data rates, shrinking the backup window in the process.

Data is stored in the virtual tape server’s internal disk storage and fed to the tape backup in the background. This is done at a speed that the tape device can handle. In this arrangement, it is possible to take faster, error-free backups.

Get your backup right

There is no use in having great hardware if you cannot make optimal use of it. Backup software is required to get the most from your backup devices.

Backup software provides functionality such as automation of data movement, monitoring, copying, backup and space management. It takes care of data replication for mirroring, snapshot capabilities, and synchronous or real-time data replication. Mirroring data to remote locations over IP networks is also possible. Available tools provide features such as bandwidth throttling and automatic scheduling. Backup and recovery tools are available for server and desktop backup.

These software tools can provide policy-based automation of storage. This is of immense help in hierarchical storage management that helps automate the movement of data from costly primary storage to lower-cost nearline storage or tape backup. Software can also prove useful for disaster recovery and restoration. Features are also present in most solutions to track storage utilisation.

Certain parameters have to be defined before selecting a backup solution. These include the storage to be backed up, the frequency, time of the day, and the media to be used.