The idea of removable disk storage isn't new. It's been around for years. Take IBM Corp. for example. The company sold a large number of disk packs to data center customers
But today's removable disk is usually an entire, standard disk drive, accompanied by special packaging to make moving it from place to place a practical and reliable proposition. And that proposition turns out to be quite appealing to many kinds of customers. In fact, according to a recent study, IDC's Worldwide Hard Disk Drive 2009-2013 Forecast, removable disk shipments worldwide exceeded 600,000 "cartridges" at the end of 2009 and a compound annual growth rate of 38.1% is expected to continue through 2013.
One flavor of the technology, RDX, produced by ProStor Systems, has even spawned the RDX Storage Alliance, a trade group for participating companies, including Imation Corp. and Tandberg Data.
RDX consists of a removable disk cartridge and an RDX dock. The cartridge has a built-in 2.5-inch hard disk drive (specific capacities vary) within a ruggedized cartridge that can tolerate a one meter drop. Current drives allow for data transfer rates of about 45 MBps. Quoted market prices for cartridges start above $150.
Another contender is the Imation Odyssey Removable Hard Disk Storage System (Imation also offers an RDX product). Similar to the RDX design, Odyssey consists of a ruggedly packaged hard disk and a docking station. Quoted market prices sometimes start at less than $100 for a cartridge.
REV is a removable hard disk storage system from Iomega, an EMC Corp. company. It differs from other removable disk systems in housing the platter, spindle and motor within the cartridge, while the drive heads and drive controller are retained in the drive. Current drives allow for data transfer rates of about 25 MBps. Market prices start at above $300 per cartridge.
Who should use removable disk storage?
According to David Hill, the principal of Mesabi Group, removable disk has a "use case" that may appeal to many people but it isn't for everyone. But one major advantage that removable disk has is that it can store data in "native format." In other words, it can store it in the same format as primary storage without worrying about proprietary or tape-specific formats or the hassle of sequential access which tape presents. "If you haven't invested in a tape infrastructure removable disk might make even more sense," Hill said.
Likewise, Greg Schulz, principal and analyst at the Storage IO Group, said the appeal for removable drives is obvious. "I back up to removable drives periodically and then I take them off site, and I do that in conjunction with backup of my local hard drive and a cloud-based backup solution," he said.
Removable disk drives vs. tape storage
Schulz said the appeal of removable disk lies in both its portability and the fact that, unlike comparable tape storage solutions, you have the option of fast random access as well as very high data transfer rates.
Schulz said removable disk is a particularly viable data backup choice for the prosumer and small-office home-office (SOHO) market. "Beyond that, it still has an important role to play," he said. For instance, he noted that remote offices and branch offices often rely on tape. Removable disk could be a faster and more appealing alternative, particularly since it can be configured to use RAID to enhance data protection. "At the lower end of the market it is an easy replacement for tape but if you are a larger organization and have already made a big investment in tape infrastructure it may not make sense," he said.
Removable disk drives' speed and portability also make them a strong contender when data backup becomes disaster recovery. Getting through a data restore would be much faster using removable disk as compared to tape.
However, Schulz warned that you won't save money relative to tape. Nor is removable disk necessarily better in other measures. "It isn't better than tape and it isn't worse -- they both face risks from magnetic sources, heat and radiation, and either could be ruined by being left in a hot car," Schulz said. Physically moving so much data around so easily could also be considered a risk with removable disk (though much the same occurs with tape). Still, Schulz said the best solution is to encrypt all of your data.
According to Schulz, the crucial differences between removable disk and tape probably come down to ease of use and speed. Removable disk storage generally wins in the category of speed -- RDX removable disk can deliver up to 40 MBps. Price and capacity are also some of the biggest differences between disk and tape. Schulz said that removable disk generally follows the overall trend in disk drives -- lagging the performance of similar capacity drives that aren't removable by about a year. "But that comes with a pricing challenge -- removable disk is not cheap," he said.
Schulz also noted that product manufacturers are also hopping on board. "Manufacturers like HP and Dell, where they might have offered an Iomega Zip Drive in the past, now are likely to include a docking station for a removable disk drive," he said. As far as the differences between different removable disk drive manufacturers, Schulz said there aren't many. "Inside the cartridges, the disk drives are just like the ones you would find in a computer or RAID enclosure from one of the major manufacturers," he said.
According to Schulz, removable disk drives also integrate naturally into most existing data backup software. "I have EMC Retrospect and it recognizes which disks are the removable ones and reminds me when to do backups," he said.
However, he admitted that standards are still lacking. Today the cartridges are tied to a particular vendor's docking system/drive, much the way products like the Iomega zip drive of the past were unique to that manufacturer. "For the most part the docking stations have a USB port, but you still need the docking station or a small portable version to use it," said Schulz. But things could change. "ProStor is trying to get the industry to standardize on their solution and they are working hard to make that broader adoption occur," he said.
So although removable disk drives are faster than tape, that doesn't mean tape should be eliminated from a data storage environment completely. "I'm still a huge fan of tape in general, especially for enterprise-type backup, said Schulz. "But removable disk is clearly becoming a great alternative for many uses."
About this author: Alan Earls is a Boston-area freelance writer focused on business and technology, particularly data storage.