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Data Recovery for RAID

How to successfully recover data from a failed RAID

Recovering data from a failed RAID can easily turn into a costly ordeal. Please read this page carefully before proceeding. If you would like to get help from experts, please consider using our fee-based RAID recovery service.

First determine whether the RAID is hardware-based or software-based. The recovery procedures are very different.

Recovering a hardware RAID

First determine if the problem is caused by the underlying RAID mechanism. If it is not, follow the simpler recovery procedures for an ordinary drive. The following causes of problem are not related to the RAID:

Virus attacks.
The volume being deleted, resized, reformatted or otherwise changed in Disk Manager or other disk management utilities.

If the problem seems to be in the RAID mechanism, determine the operating state of the RAID and take the appropriate actions.

Avoid the most common mistakes that may cause data to become unrecoverable.

Hardware RAID operating states
Status			Prognosis	Suggestion
RAID controller	Disk Manager	Windows Explorer	Prognosis	Suggestion
Current status is normal. No controller or disk errors. No recent change in RAID configuration.	RAID is displayed as a single disk. Volume configuration has not been changed (screenshot).	Volume is inaccessible or accessible with missing files.	RAID mechanism is operating normally. Problem may be unrelated to RAID.	Follow recovery procedures for an ordinary drive.
	RAID is displayed as a single disk. No drive letter or unformatted volume (screenshot).
	RAID is displayed as a single disk. Volume has been deleted, reformatted, resized (screenshot).
Current status is degraded.	RAID is displayed as a single disk. Disk Manager is not aware of degradation (screenshot).	Volume is accessible	RAID is degraded due to a disk failure	Follow recovery procedures for a degraded hardware RAID.
Current status is normal. RAID failed and was rebuilt unsuccessfully.	RAID is displayed as a single disk (screenshot).	Volume is inaccessible or accessible with missing files.	RAID is broken.	Follow RAID reconstruction procedures.
Current status is normal. RAID settings have been changed.
Current status is normal. Disks have been reconfigured and disk order may have changed.
Abnormal RAID status such as "offline", "inactive", "undefined", etc. There may be disk or controller hardware errors.	RAID is not displayed. Sometimes the individual member disks are displayed as unformatted disks (screenshots).	Volume is inaccessible.

Recovering a software RAID

Virus attacks.
The volume being reformatted.

If the problem seems to be in the RAID mechanism, determine the operating state of the RAID and take the appropriate actions.

Note that a RAID 0 is also referred to as a striped volume.

Software RAID operating states
Status		Prognosis	Suggestion
Disk Manager	Windows Explorer	Prognosis	Suggestion
RAID status is normal (screenshot). RAID configuration has not been changed in Disk Manager.	Volume is inaccessible or accessible with missing files.	RAID mechanism is operating normally. Problem may be unrelated to RAID.	Follow recovery procedures for an ordinary drive.
Volume has been reformatted. RAID configuration has not been changed in Disk Manager.	Volume is inaccessible or accessible with missing files.		Follow recovery procedures for an ordinary drive.
RAID status is degraded (screenshot)	Volume is accessible	RAID is degraded due to a disk failure	Use Disk Manager to repair the RAID.
Current status is normal. RAID failed and was rebuilt unsuccessfully.	Volume may be inaccessible or accessible with missing files.	RAID is broken.	Follow RAID reconstruction procedures.
Current status is normal. RAID settings have been changed.
Current status is normal. Disks have been reconfigured and disk order may have changed.
RAID is not displayed. The disk extents comprising the RAID are usually displayed as unallocated disk space (screenshot).	Volume is inaccessible

What is a RAID?

RAID (Redundant Array of Inexpensive Disks) is the organization of multiple disks into a larger logical disk for better performance and/or availability. There are many levels of RAID of which we will discuss the two relevant levels 0 and 5.

In a RAID 0 (or striped volume) data is striped across all disks in a rotating pattern. A RAID 0 with two 20-GB disks will function as a single 40-GB logical disk. There is no redundancy. If any disk fails, data is lost and cannot be recovered.

In a RAID 5 data is also striped across all disks in a rotating pattern but with parity data for redundancy. A RAID 5 with three 20-GB disks will function as a single 40-GB logical disk. Parity data uses up the equivalence of one disk.

A RAID 5 becomes degraded when one disk fails. The RAID, however, still functions because the data on the failed disk can be regenerated using the parity data on the remaining disks.

What is a hardware-based RAID?

A RAID is considered hardware-based when it is implemented in hardware, either on the motherboard directly or a separate RAID card. Windows views the entire RAID as a single disk. The individual member disks are controlled by the RAID controller and not directly accessible to Windows. An example of a hardware RAID 0 is depicted in the screen snapshot below.

A RAID 0 implemented in hardware

Disk 2 (drive D): A hardware RAID 0 comprising two 18.68-GB disks is displayed as a single 37.35-GB disk.
(Disk 0 and 1 are irrelevant.)

What is a software-based RAID?

A RAID is considered software-based if it is created in Windows using the Disk Manager. Windows has direct access to both the entire RAID and the individual disks. An example of a software RAID 0 is depicted in the screen snapshot below.

A RAID 0 implemented in software

Volume D: A software RAID 0 (striped volume) comprising two 18.68-GB disks.
(Disk 0 and 1 are irrelevant.)