by W. Curtis Preston
What role should tape have in a backup system? To answer that, we must first talk about the streaming nature of tape. Tape drives are designed to go very fast, and when they are not run at that speed, they do not perform as desired. For example, an LTO-4 drive has a native transfer rate of 120 MBps. If you consider that most open-systems environments average 1.5:1 compression, that means that effective throughput of an LTO-4 is 180 MBps, yet very few environments run their tape drives at this speed. When you use a 180 MBps tape drive to write a 30 MBps stream, or even an 80 MBps, it spends a good deal of its time going back and forth (backhitching, as it's called) to keep up with that slower data rate. If it backhitches a lot, we call it shoe-shining, because the actions of the tape wheel mimic that of a person shining their shoes.
Wherever you're using tape storage, the key is to supply a stream fast enough to keep it happy. The first thing that some backup software products do is to use multiplexing, where multiple backup streams from different sources are interleaved together to create a faster backup stream. This helps the backup, but it does not help the restore, as all that extra data from the other streams must be read and discarded when you are restoring just one stream.
The next thing that backup products started doing was LAN-free backup. Since one of the problems with creating a fast stream was that the data was being sent across the LAN, backup vendors started allowing users to connect larger backup clients to the SAN and back up their data directly to tape. This helps the backup go much faster by eliminating the creation of all those network packets. However, there is still a challenge when reading from random-access, fragmented disks as the source for the backup image.
This is why many customers have stopped using tape as the primary protection mechanism for backups. When you're backing up across the LAN, or even when copying data on random-access, fragmented disks, you simply can't supply the data fast enough to keep that tape drive happy. The solution that most people have started using is to first back up to disk and then copy to tape. This action serializes the backed up data together and allows you to then copy it much faster to tape and keep the tape drive happy. This is especially true with incremental backups that would otherwise hold onto a tape drive for hours and give it only a few gigabytes of data. Now they can "hold on" to a file or a virtual tape drive for hours, then turn around and copy those few gigabytes of data to tape in just a few seconds.
Tapes must be encrypted if you send them offsite. There are a number of options, such as replicating deduplicated backups, continuous data protection (CDP), and near-CDP, but suffice it to say that the three rules of encryption are key management, key management, and key management. Lose your keys and lose your data.
The long-term future of tape is unsure. We are starting to have solutions that offer onsite and offsite backups without using tape, and more users are using these systems every day. Customers are also using technologies like CDP that don't even work like traditional backup. However, if a company is considering tape in the short term, it is unlikely they will find themselves doing the equivalent of buying an HD-DVD player a year ago. Tape isn't going away any time soon.
More resources on tape backup and recovery
Getting the right tape library takes preparation. An expandable, modular tape library supported by sophisticated management features and tied to modern backup software will support your enterprise for years to come. It's worth taking the time and effort to make the right choice. Read this article to learn how to choose the right tape library.
Careless tape handling can cut the lifespan of a tape to weeks, or even destroy a tape entirely. To get the most of out your tapes, it's important to handle them carefully and store them properly. Read this article to learn how to care for your backup tapes.
Designing a new backup system is not always a rip-and-replace exercise. Unless you wake up one morning and realize you need a solution to back up 50 TB of newly found, never before backed up data, chances are good you have an existing and potentially significant investment in tape technology that you can't necessarily part with that easily. This tip discusses tape storage today.
W. Curtis Preston (a.k.a. "Mr. Backup"), Executive Editor and Independent Backup Expert, has been singularly focused on data backup and recovery for more than 15 years. From starting as a backup admin at a $35 billion dollar credit card company to being one of the most sought-after consultants, writers and speakers in this space, it's hard to find someone more focused on recovering lost data. He is the webmaster of BackupCentral.com, the author of hundreds of articles, and the books "Backup and Recovery" and "Using SANs and NAS."
This was first published in March 2009