Removable hard disk drives (HDDs) deliver the faster data backup and recovery times associated with storage systems used in enterprise storage area networks (SANs) and also provide the portability and infinite capacity features of tape to meet corporate offsite data retention and recovery requirements. But removable HDDs have yet to penetrate the enterprise market, finding a niche rather in direct-attached storage (DAS)-only environments as an alternative to tape-based backup and recovery.
A recent Enterprise Strategy Group survey found that approximately 14% of companies still only use DAS for their storage needs -- the segment of the market that's primarily using the current generation of removable HDDs and associated disk docking stations. Using removable HDDs to protect these DAS-attached servers gives companies some distinct advantages vs. using locally attached tape devices. These advantages include:
- Removable HDDs may be used as a normal disks for extra online capacity if needed.
- The disk docking station may present a persistent disk drive letter or volume to the host operating system, even when there is no removable disk cartridge in it.
- Removable HDD capacities are as large or larger than internal HDDs so full backups can occur without swapping disks out during a backup.
- A disk docking station may concurrently host multiple removable HDDs (up to eight) for servers with extremely large amounts of data to back up.
Removable HDD systems are available in two distinct categories: those that use disk cartridges, and others that use off-the-shelf HDDs. Disk cartridges (such as the RDX and Quantum Corp.'s GoVault formats) use 2.5-inch HDDs like the ones used in laptop PCs. Manufacturers encase these HDDs in durable plastic cartridges so they can withstand drops, transport, ejections from the disk docking station and frequent handling. Disk cartridges may also include other features such as status lights to indicate when the disk cartridge is in use and protection to keep users from touching recessed connectors that can cause static discharges.
Of the two disk cartridge formats, the RDX format has emerged as the early market leader, accounting for approximately 90% of the removable HDD sales, according to IDC. RDX is also licensed and distributed by manufacturers like Dell Inc., Imation Corp. and Tandberg Data, whereas the GoVault is manufactured and distributed solely by Quantum.
Click here to download a chart detailing key features and considerations of removable hard disk drives.
Because disk cartridges use smaller 2.5-inch drives, their capacities are typically lower than the 3.5-inch HDDs found in the newest servers, so it may require more disk cartridges to back these servers up. Also, disk cartridge capacities will be behind the general availability of higher capacity 2.5-inch HDDs by six to 12 months as disk cartridge manufactures first need to obtain 2.5-inch HDDs and prepare them for distribution in their disk cartridges. Additionally, users will pay a two to three times per gigabyte premium over the cost of off-the-shelf HDDs.
Small businesses that need higher capacities and lower costs should consider companies such as Idealstor, which provides caddies that convert off-the-shelf HDDs into removable HDDs for its backup appliances. An off-the-shelf HDD is inserted into the caddy (that cost approximately $35 per caddy), which fit into slots on Idealstor's backup appliances. The caddy protects the pins on the HDD during handling, insertion and transport and helps to extend the life of the HDD.
But this approach has its downsides, too. Users need to absorb a higher upfront cost because they must first introduce Idealstor's appliance into their environment, which comes with its own backup software. Also, if users anticipate handling and moving the caddies a great deal, these units are less well equipped for regular handling and transport than GoVault and RDX disk cartridges.
Companies using DAS can still take advantage of disk-based backup. Removable HDDs give these companies the same options they have using tape with all of the performance benefits of disk. If continuing to use your current backup software and frequent handling and transport of removable HDDs are expected, then disk cartridge formats make the most sense. However, if the labor of inserting off-the-shelf HDDs into caddies is acceptable, caddy movement is infrequent and you can use the vendor's provided backup software, then backup appliances with off-the-shelf HDDs are a viable option.
About the author: Jerome M. Wendt is lead analyst and president of DCIG Inc.
This was first published in June 2008