By Mark Ferelli
Like any storage or networking technology, some degree of management is required to make sure that a tape library continues to provide reliable recovery of vital business records and information. And data-center veterans know that faulty tape media is a potential source of permanent data loss.
Storage administrators who manage backups and archives spend significant time managing tape media and the information it holds, but still find it a challenge to ascertain much-needed information about tapes and to ensure the protection of the data on tapes.
- How many times has a tape been used?
- Where did it come from, and when?
- Has it experienced any errors?
- Is it nearing a time when you should retire it to protect your data?
Nathan Thompson, CEO at Spectra Logic, points out that these questions relate directly to the lifecycle of the tape media as well as the data-protection imperative. Addressing what he calls “media lifecycle management,” Thompson points to cassette-based memory features that can store relevant metadata about the cassette itself as well as the data it contains. The in-cassette feature tracks critical data points for each tape, including the number of loads, errors, and details on the drives and partitions the cartridges were used in.
In the late 1990s, Sony introduced a semiconductor memory element called Memory-in-Cassette (MIC) in its AIT tape cartridges. The MIC is a memory chip built into the data cartridge that provides a direct connection to the drive’s on-board processors, which speeds access to files and cartridge data, and holds the system’s log and other user-definable information.
LTO tape cartridges now offer similar technology, called Medium Auxiliary Memory (MAM).
Information and file-search parameters are formatted within the MAM system, rather than using the on-tape index file or requiring the time-consuming media load and tape threading process historically used by other tape technologies. Data access time is effectively cut in half—regardless of tape drive speed and recording density. MAM is typically implemented as a non-volatile memory chip mounted inside the tape cartridge shell that can be accessed via an RF interface.
Tape media duty cycle
With tape media, you often don’t know that a tape is bad until it fails—at which point it’s too late. As a result, the most typical way that this issue is addressed is to pull tape media out of circulation after a certain amount of time and assume it is unreliable even if it has not had any errors. This would be considered its useful duty cycle. Some data centers that use linear tape daily pull tapes out of circulation after about a year.
Most backup/recovery products have the ability to enforce a tape duty cycle by attributing an expiration date to the tape media using the backup software.
A tape’s reliability is also dictated by how long it has been sitting: its archival or shelf life. This doesn’t come up as often with respect to tape reliability, mainly because of the long shelf life that most modern tapes can have. For example, depending on temperature and humidity, LTO-4 has an archival life of about 30 years.
The best way to prolong tape media’s duty cycle is to avoid having errors altogether. Errors are usually the result of damage to the physical media within the tape cartridges, rather than a result of defects on the media. This damage to the media typically occurs because of incorrect tape handling procedures.
One common problem is edge damage. If a tape is dropped, the edges of the media could get crimped. With older linear tape products, the edges served as servo tracks (a track that allows the tape drive head to stay aligned with the tape) so it was possible that media errors could result because the head could no longer “stay on track.” LTO eliminated this issue by means of a series of pre-recorded servo tracks, and is relatively impervious to handling damage.
The best media management products—software or hardware—are useless if not regularly used. Establishing “media lifecycle management” should become a key part of storage administrators’ management responsibility, especially those responsible for archival and backup services.
Combining a backup-and-restore plan with the tips below can help ensure your data will be accessible in the future, even if disaster strikes. A tape-based backup and restore plan will depend on a number of factors:
- How often does your company need to refer to its data? If you need to refer to yesterday’s data, a daily tape rotation would work best.
- How valuable is your data? The more valuable the data, the more often you should back up and move tape media off-site.
- When you use tape cartridges to back up your files, be sure to follow a regular tape backup rotation.
- Make sure that all tapes are uniquely identified.
- Use specifically identified tapes for incremental backups, and use other tapes for each of the weekly backups. Use yet another set of tapes for monthly backups, rotating these each month. Then store the long-term archival tapes at a secure off-site location as part of a disaster recovery and business continuity program.
The physical media in your tape library needs thoughtful care as well. You should pay attention to the operating environment recommended by the media manufacturer. Other issues for tape cartridge care include the following:
- Allow tapes to acclimate to the operating environment—one hour for each hour spent off-site, for a maximum of eight hours.
- Regular cleaning removes debris from drive heads. Most tape vendors offer dry cleaning cartridges that do not require chemicals or solvents.
- Store tapes in a dark, cool, dry place, away from equipment. Do not leave used cartridges in the drive; place them in their final storage box so the reel axes are horizontal.
- Tape cartridges must be kept free from contamination. Do not expose the cartridges to dirt, dust, or moisture. Do not open the cartridge access door and touch the tape. Do not use the cartridge beyond the recommended life.
- Always remove cartridges from the drive when not in use, and store cartridges in protective plastic cases. Never remove cartridges from the drive when the drive LED light is on or blinking, indicating that the tape is moving.
- Keep tape cartridges away from direct sunlight and other heat sources. Verify that cartridges are not exposed to temperature extremes during the time that they are transported to and from remote storage.
- Keep cartridges away from sources of electromagnetic fields, such as bulk erasers and magnetic tools. Do not bulk-erase preformatted cartridges, because the servo information cannot be reformatted by the tape drive and it will render the cartridge unusable.
If a cartridge is dropped it can misalign or permanently damage the tape guiding components inside the cartridge and possibly render the cartridge unusable. If a cartridge has been dropped, it may be suitable for a single use. It is recommended that the data on a dropped cartridge be copied to another cartridge. First the cartridge might need to undergo a re-tensioning pass. Once the data has been copied to a new cartridge, the dropped cartridge should be discarded.
Mark Ferelli is a freelance writer. He can be contacted at firstname.lastname@example.org.
Backup versus archive
Backups are used to restore an application or dataset to a specific point in time. They are incremental operations, where copies of data are typically retained a limited amount of time (e.g., a few days) until a new incremental backup is created.
HP, Sony to extend DAT/DDS
Hewlett-Packard and Sony announced last month that they will extend the Digital Audio Tape (DAT) tape format into the next generation. The DAT 320 format will provide a backup speed of 86GB per hour—assuming 2:1 data compression—and have a capacity of 320GB per cartridge with 2:1 compression, or twice the capacity and transfer rate of the DAT 160 predecessor. DAT 320 will be backward-compatible with DAT 160.
DAT is also known as Digital Data Storage (DDS), or sometimes DAT/DDS.
Sony’s participation in the DAT 320 format marks the re-entry of the vendor into the DAT/DDS market. Both HP and Sony will manufacture DAT 320 drives, and media is expected to be available from a variety of vendors, including Fuji, Imation, Maxell, and Sony.
Although HP and Sony are jointly developing DAT 320, the two companies will manufacture their own product lines. DAT 320 products are expected in the first half of 2009, according to Bob Wilson, vice president of storage platforms in HP’s StorageWorks division. The drives are expected to be available with USB and SAS interfaces. —DS