As part of my job, I am sometimes confronted with backup issues as well as aspects of “data archeology”. For example, a while ago I had to restore some 10-year old data from our tape archive. Luckily, the tapes were stored in an electromagnetically shielded vault and were all still readable. That was, after spending days tracking down our last remaining compatible tape drives and figuring out how to get them to work again. I thereby learned quite a bit about the various tape formats used throughout the past two decades – and got reminded why I used to hate tapes in the first place. This got me wondering: What role do tapes still play today, and what are their prospects for the future?
StorageSearch.com is an interesting Web site to learn all sorts of fun-facts about the pros and cons of various storage technologies. The site describes itself as an “enterprise storage focused Web directory since 1998”. Today, most new articles on StorageSearch.com appear to solely focus on Solid State Storage (SSD). But in the past, a significant amount of attention was given to other storage technologies as well, especially hard disks, optical storage, and tapes. A big discussion in the early 2000s was around the pros and cons of then relatively new disk-to-disk backup versus tape. Steve Garner summarized and compared some different views on this subject in his StorageSearch.com article: “Disk to Disk Backup versus Tape – War or Truce?” Seven years later, a 2004 article may appear outdated, but in this case, I think that many major points are still valid. Garner argued, that “disk-to-disk backup looks like a new edition of Hierarchical Storage Management (HSM)”, offering fast backup and recovery to a relatively costly medium, which should be complemented with less frequent traditional tape based backup for longer term archival. He did however envision that disk-to-disk backup might be more than this, and that it offered the potential of replacing tape eventually.
All the advantages of tapes and removable discs versus hard disks seem to boil down to the fact that they are naturally removable media. Although hard disks can be mounted to be easily removable as well, one is still removing the entire disk drive, not just the storage medium. (Of course there were various technologies involving removable magnetic disks, such as floppies and ZIP drives, but they lacked the high areal density, speed, and reliability of hard disks, and nowadays are all obsolete.) The removability of the storage medium allows the medium to be relatively cheap (but the drive may be still expensive), easy to transport, and easy to store. On the other hand, transporting mechanically complex hard disks is considered very risky, and their long-term storage may involve other aging factors (capacitors, bearing lubricant) beyond magnetic decay and leakage. A tape that gets exposed to water, dust, or smoke may be still salvageable, a hard disk less likely so.
Traditionally, tapes had the advantage of being cheaper than disk arrays when large amounts of data needed to be stored. This was due to the relatively low price of tape cartridges compared to hard disks, which quickly offset the high initial price of the tape drives. However, falling disk prices versus nearly stagnant tape prices have been eroding this advantage.
In another StorageSearch.com article from 2003, John Woelbern from Sony Electronic’s Tape Storage Solutions asked, whether tape backup had a future. He argued that to remain competitive, tapes would need to reach capacities around 1TB per cartridge by 2006 and around 10TB per cartridge by 2011. He went on to advertise Sony’s then new SAIT system, predicting that it would be able to meet and exceed these demands within the given timeframes. Today we are in the year 2011, and SAIT has not surpassed 800 GB per cartridge, while its biggest competitor, LTO-5 has barely managed to reach 1.5 TB per cartridge (all capacities uncompressed). By comparison, hard disks have just reached 3 TB per drive, thereby clearly surpassing tape storage density.
I searched some online retailers and found the following prices: An LTO-5 cartridge costs about $60, an entry-level LTO-5 drive about $2500. A 3 TB hard disk costs about $280 (probably half of that within a few months). Assuming all other hardware and software components to cost roughly the same for tape and disk solutions, this indicates that tape technology may be still cheaper than disk technology, but only if storage requirements are greater than about 47 TB. Ergo, tape backup might still make sense for huge datacenters, but for many small and medium sized businesses, disk-to-disk backup has already become a significantly cheaper alternative.
I believe that tape backup will not fully disappear any time soon, but will continue to retract into a niche market: Large data centers will still view tape as a cost effective backup medium, especially if long-term archival is crucial. However, smaller businesses will move entirely to cheaper, faster, and easier to maintain disk-to-disk backup. They may continue to use tape backup indirectly though: as a backup of their backup’s cloud based backup. Outsourcing tape backup to the cloud gives the small guys access to better economies of scale – and lets someone else deal with the tapes.