Data recovery FAQ: answers to your questions
Find answers from our specialists to the most frequently asked questions about data recovery: hard drive failures, SSD, RAID, USB drives, pricing, turnaround times and process. SOS Data Recovery (Tesweb SA), Swiss specialist since 2006 with over 10,000 cases handled, answers your questions.
Why consult our data recovery FAQ?
Our technicians answer the most frequently asked questions about hard drive, SSD, RAID, NAS, USB drive and memory card failures. Each answer is based on over 10,000 cases handled since 2006 and regularly updated. If you cannot find the answer to your question, contact us — free diagnosis within 3 hours.
JBOD: One or more disks are defective
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: One or More Disks Failed — What to Do?
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: One or more disks are faulty — what to do?
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: A hard drive is defective
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: At least 2 hard drives are defective - what to do?
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: At least 3 hard drives are defective — what to do?
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: One or two hard drives are defective
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.
RAID controller failure
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 in Degraded Mode: Causes, Risks, and Solutions
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.
RAID is no longer detected by the computer
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