We can supply you with a number of removable drives, from USB keys to Large Solid State removable Drives for casual use, all the way up to multi-terrabyte SAN and NAS Devices.
The Enterprise class devices are set up with built-in drive redundancy, and can be set up to automatically replicate to other devices for further data protection.
Some of the hardware redundancy levels are:
RAID - Redundant Array of Inexpensive Disk. - The name's been around since the 70s, when mainframe hard drives were in the 10s to 100s of thousands of dollars each. SCSI (Small Computer System Interface) allows for inexpensive disks to be manufactured and used to mirror or strip data onto multiple disks.
RAID Level 1 - Mirroring - having a duplicate copy of a hard drive, so if one fails, the other has a complete copy of the data and nothing is lost.
RAID Level 0 - Striping - No data security at all, but it speeds up data access. It entails 2 or more hard drives that it splits the data between. Reading from multiple disks reduces the time required to access and transfer the data.
RAID Level 5 - Striping with parity - All the advantages of striping, but with data security. It requires 3 or more drives, and it uses 1 drive as a parity drive. This way, one drive can fail, and the data is still intact.
RAID Level 6 - Striping with dual parity - Similar to Raid-5, but it has dual parity drives, allowing for two drives in the set to fail simultaneously, without any data loss. This requires 5 drives to implement.. 3 data drives, and 2 parity drives. If you only have 4 drives, and you want this kind of protection, see mirroring (Raid-1) optionally with striping (Raid-10)
Other common configurations are RAID Level 10 - Raid Level 0 (striping over multiple drives) with Raid Level 0 (mirroring the entire set of drives). With this configuration, you would have to lose at least 4 hard drives at once before any data was affected, and at that, they would need to be 2 drives from the first striped set, and the exact same 2 drives from the mirrored set. Since it is statistically highly improbable for this to happen, this system is very safe and secure.