Briefing Note

Eric Slack, Senior Analyst

Spectra Logic is a client of Storage Switzerland

The storage industry has had systems to monitor the integrity of data stored on various media, from SSDs to spinning disks, for a number of years. In the archive space, this approach has been used by disk system manufacturers to provide assurance that data stored for long periods of time can be read. But disk drives consume power, continuously, so technologies like MAID (Massive Arrays of Idle Disks) which turn drives off when not in use, have again become popular. Interestingly, by powering down inactive drives, the storage industry seems to be making archive disk more like tape. Tape on the other hand is a natural fit for archive data. It doesn’t consume any power when not being accessed and has a capacity per sq. ft. of data center space that disk drives are dying for.

It’s prudent to verity the quality of assets over time. Like old bottles of wine, companies that rely on their reference data need to make sure these assets haven’t ‘turned to vinegar’ while sitting on the shelf. Up until now, spinning disk has had the advantage of built-in data verification. To provide this assurance for tape, Spectra just introduced BlueScale Data Integrity Verification, a feature that’s available on all new libraries and as a no-cost upgrade for existing customers. Here’s how it works:

Step 1 - PreScan

Spectra libraries compile a database of information about each tape, such as the number of times it’s been loaded and its accumulated read errors. These data can red flag an old piece of media that is nearing the end of its useful life. In the PreScan step, the library checks each newly imported tape cartridge to confirm its age and health and assure it’s ready to accept data.

Step 2 - Quick Scan

This process runs a 1-minute checksum scan of the first track on a cartridge, essentially  a confirmation that data was successfully written to the tape during the last write cycle. Sometimes software applications that manage tape drives can miss a failure, such as a stuck tape or broken leader. These are rare, but can be found quickly with this step and replaced before the next write operation.

Step 3 - PostScan

This step is typically run on every cartridge, every 12 months or so and does a checksum scan of the entire tape to identify any locations with uncorrectable errors. This longer, ongoing process verifies every cartridge on a rotating basis and is managed by the library and run during periods where resources are available. Together with the PreScan and QuickScan steps, media health and data integrity can be maintained on an archive of any size, transparently to the users and applications which rely on it.

Storage Swiss Take

As reference data sets grow and IT becomes aware of the power and floorspace consumed by these critical assets, tape’s becoming fashionable, again. It’s density is remarkable, but in the final cost analysis, there’s nothing like a storage medium that can be turned off. Rather than trying to make disk more like tape (MAID), big data users are instead turning to tape. Backup failures are frustrating but archive failures can be deadly. In the archiving space, Spectra’s Data Integrity Verification is making tape even more appealing.