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Overcoming tape’s limitations
Reliability improvements are a “must” if tape is going to continue to be a key recovery technology in the face of ever more stringent recovery time objectives (RTOs) and recovery point objectives (RPOs). The use cases for magnetic tape have remained constant for nearly 50 years largely because its limitations have also remained constant. To appreciate the magnitude of new tape technologies, it’s important to understand these limitations.
- Media degradation. Although
- tape media reliability has improved dramatically, best practice still dictates that media should be periodically tested and rewritten. That’s a daunting task when tens of thousands of media elements are archived. The failure of a critical data block, such as the index block, can render the entire tape unreadable.
- Drive compatibility. Although LTO maintains backwards-read compatibility, the archive requirement for the media may exceed the supported life of the drive and media. Occasionally, a tape written on one drive can’t be read on another drive. Recovering this data years later can be time consuming and costly.
- Lack of interoperability. LTO media can’t be read in non-LTO drives and vice versa. This has stymied many a data transfer effort.
- Proprietary tape formats. Although tar and cpio are industry-standard tape formats, they’re rarely used in their pure and interchangeable forms. B/R vendors use their own formats for efficiency reasons. Consequently, the tapes can only be read by that B/R application unless specifically written in tar or cpio.
- Backwards compatibility. Many IT users have a mix of media types in the vault due to technology and product generational changes. Being able to read all the various media types means maintaining not only legacy tape drives, but legacy servers, operating systems, drivers, interfaces and B/R versions. The possible permutations needed to read a seven-year-old tape makes recovery problematic at best, and very expensive and time consuming if even possible.
In addition to the low cost of storage, tape has the advantage of very high transfer rates. With LTO-5 streaming at 280 MBps, or roughly 2.2 Gbps, a single 10-drive library requires multiple 10 Gigabit Ethernet (GbE) pipes to keep up. This may not be a big deal within a data center, but it’s a serious issue for rapid recovery of large data repositories over a wide-area network (WAN). When restoring terabytes of data, tape libraries are the hands-down choice over the typical 1 Gbps link, or even multiple Gbps links.
This was first published in February 2012