FAQ

JBOD (Just a Bunch Of Disks) is an aggregate of multiple hard drives operating in sequential writing. Unlike RAID 0, data is written entirely to the first hard drive in the aggregate. Once it is full, writing continues on the second disk, and so on until the last disk in the array.

Consequence in case of failure: If a defective disk contains data, it is inaccessible until the disk is repaired or replaced. Unlike RAID 1 or RAID 5, JBOD offers no redundancy: the loss of a disk results in the loss of all the data it hosts.

RAID 0 is a storage configuration that distributes data in blocks across multiple hard drives simultaneously (a technique called striping). Each file is fragmented into several pieces distributed across all the disks in the array. In the absence of redundancy, the failure of a single disk renders 100% of the data inaccessible, as the missing fragments make each file incomplete and unreadable. According to industry statistics, the risk of total data loss in RAID 0 is proportional to the number of disks: a 4-disk RAID 0 quadruples the risk of failure compared to a single disk.

RAID 1 is a mirrored storage configuration in which each piece of data is written simultaneously to two or more disks, providing complete redundancy. If one disk fails, the data remains accessible on the intact mirror disk(s).

RAID 5 is a redundant storage configuration that distributes data and parity across a minimum of 3 hard drives, allowing for the failure of a single drive without data loss. If one of your drives is defective, your RAID 5 remains functional but switches to degraded mode: all data remains accessible, but any additional failure would result in total data loss.

RAID 5 is a redundant storage configuration that tolerates the failure of only one disk at a time. When at least two disks fail simultaneously, the integrity of the array is compromised and the RAID is no longer functional: the data is no longer accessible by normal means.

RAID 6 is a redundant storage configuration that tolerates a maximum of 2 simultaneous disk failures thanks to its double parity. When at least 3 disks are defective at the same time, this tolerance is exceeded: the RAID 6 volume is no longer functional and the data is no longer accessible by the usual means.

• RAID 6 fault tolerance: 2 defective disks maximum
• Your situation: ≥ 3 defective disks — critical threshold exceeded
• Immediate consequence: automatic reconstruction impossible, risk of total data loss

RAID 6 is a RAID level that uses dual parity, allowing a set of at least 4 hard drives to continue functioning even if one or two drives fail simultaneously. In this case, your RAID enters degraded mode: the data remains accessible and intact, but the tolerance for additional failures is reduced or non-existent until the failed drives are replaced.

A failed RAID controller is a hardware failure that prevents the operating system from detecting and accessing the entire RAID volume, making all data inaccessible until the failed component is replaced or bypassed by a specialist. According to Ontrack's data recovery statistics (2024), controller failures account for approximately 20% of cases of loss of access to RAID systems.

RAID degraded mode is a critical state in which a RAID controller reports that one or more disks in the group are no longer functioning correctly, reducing data redundancy without necessarily interrupting service. According to Backblaze statistics (2024), 5.1% of hard drives fail each year, making degraded mode one of the most frequent RAID alerts in a server environment.

The system generally remains operational in degraded mode, but any additional disk failure can lead to total data loss. Rapid intervention is imperative.

A RAID not detected by the computer is a critical situation that occurs when the RAID controller is defective or its configuration has been lost, making the entire RAID volume inaccessible to the operating system.

The main causes of an undetected RAID include:

• Defective RAID controller: The card or chip managing the RAID no longer responds, preventing any communication with the disks
• RAID configuration loss: The metadata describing the RAID structure (type, disk order, block size) has been erased or corrupted
• Power or connection problem: A faulty cable or unstable power supply can make the RAID invisible at startup