Disk vs. Tape Storage: Is Tape Cheaper and Better?
By Drew Robb
February 28, 2011
Not so long ago, a startup known as Data Domain
(now owned by EMC) ran a Tape Sucks campaign as a means of publicizing its disk-to-disk (D2D) deduplication/backup appliances. The tape industry, being longer in the tooth and far more conservative, is never likely to be so bold. But if you listen closely, you can hear some administrators muttering Disk Sucks at least for certain applications.
While advancements in disk reduction technologies like deduplication have improved the overall total cost of ownership (TCO) of disk, tape is and will continue to be the best medium for many use cases in end users storage environments, said Mark Pastor, strategic business manager for Quantum Corp. Any time data needs to be kept for months or years, such as for compliance reasons, tape is a much less expensive medium than disk, even dedupe disk and a more reliable long-term storage medium.
A recent Clipper Group study supports this assertion. Clipper found that for an archiving application over a 12-year period (which includes updating and replacing technology during that period), disk uses 238 times more energy than tape and is more than 15 times more expensive.
Pastor asserts that tape is the best location for secondary storage in a tiered environment. For data that can be classified as less time-critical, tape is best in a larger data capacity environment, he said, with only negligible impact to the end user.
There is a tradeoff, of course, of overall storage costs versus time to data. But this shouldnt be much of an issue for infrequently accessed files. In addition, very large files such as databases or huge media files can be streamed to tape at full tape speed and vice versa without needing to repetitively seek for smaller components of the data, as happens with disk.
For this reason, many users find it attractive to prioritize tape as the medium of choice for backing up these large files, said Pastor. You get all the cost benefits of tape without the performance penalties normally associated with smaller random file storage.
Portable workflow is another area where tape might regain some lost ground, particularly in the media and entertainment space. Pastor said that Linear Tape File System (LTFS) solutions are coming to market where a tape cartridge can be utilized as a portable container for very large files that can transported from one shop (representing one part of the workflow) to other locations.
He gives the boot to the widely hyped concept of tapeless backup, too.
D2D backup becomes less effective as data in the users environment grows and as very large files are part of the backup set, said Pastor. Unless the user cannot consider different SLA levels for segments of their data, money will be wasted at some point where overall data capacity is large, if tiered storage including tape is not employed.
Not surprisingly, tape manufacturer Spectra Logic concurs with this view. Jon Hiles, the companys senior product manager, believes that tape is stronger than disk in a couple of areas disaster recovery (DR) and archiving.
For DR, he said that tapes portability and low cost give it the edge.
Getting to a recovery site with large quantities of data electronically is time consuming and expensive with even the fattest pipe, said Hiles. Tape cant be beat for large scale data movements like those which may be required in a disaster (or for general DC relocation).
The logic is simple. Those that cant afford the bandwidth or time to move large quantities of data electronically should look at porting tapes as an option. Its less expensive and less prone to damage than loading and moving entire disk arrays or storage servers to the recovery site.
Some, though, believe that the solution is to electronically vault data in, and recover from, a third-party cloud site for data recovery. Hiles counters with a security argument. How can users ensure that data moved to a cloud is securely and verifiably (from a regulatory standpoint) separate from other users data? And how can users be assured that only they have full control of and access to their data?
With disk, these questions can loom large since hard segregation of user data being shared on a disk platform is more difficult to accomplish than is the case with tape, said Hiles. Customers using tape can put their data on discrete tape cartridges housed within physical libraries at co-located recovery sites. Doing the same with shared disk arrays is difficult at best.
On the archiving side, he outlined a similar view to Pastor about overall cost and energy savings. But he added longevity into the equation. According to Hiles, tape media has been demonstrated to have a useful life of 30 years. Yes, but the tape drives used to back it up 30 years ago are probably no longer around.