Monday, 27 April 2015

How to recover data from RAID 0, 1, 5, 6, 10 configurations?

The traditional data storage configuration system has been replaced by RAID in majority. The RAID configuration let you store large amount of data with enhanced features such as: data protection, reliability, availability, performance. Sometimes you may lose access to your RAID data due to various reasons such as: Hardware failure, drive corruption, array failure etc.

You can find here information about various RAID configurations and later on, we will discuss how to recover data once the RAID architecture fails or become inaccessible.

About RAID configurations:

The term RAID refers to redundant array of independent disks.
The configuration is based on the concept of storage virtualization. Virtualization means dividing the system resources among different applications. A storage system is basically a storage array or disk array or a filer. Storage virtualization uses virtualization to enable better functionality, data redundancy, performance improvement and more advanced features in computer data storage systems. RAID uses the concept of storage virtualization for combining multiple disk drive components into a logical unit.
Using this kind of methods, the computing and data processing gets faster. Along with these, it also provides better data protection, reliability, availability, performance, and capacity features.
Based on architectures, RAID is divided into different levels: RAID 0, RAID 1, RAID 2, RAID 3, RAID 4, RAID 5, RAID 6 and RAID 10 etc.
Different RAID levels are explained below:

RAID 0: It is also known as a stripe set or striped volume. Data is distributed evenly between two or more striped disks that act as a single large logical disk. No redundancy, mirroring, parity is used. As there is no redundancy, if one drive fails the whole RAID volume fails.

RAID 1: The data of the drives are copied/ mirrored exactly on two or more disks. If one drive fails the RAID still keeps working as the same data is present on the other mirrored copy of the disk from where it can be accessed. No parity or striping is used.

RAID 2:  Bit-level striping is done rather than block level. The disks work in synchronization such that each sequential bit is on a different drive. Hamming code is used for error correction.

RAID 3: In this case, Byte level striping is done. The disks work in synchronization such that each sequential byte is on a different drive. For each corresponding byte parity is calculated and stored on a dedicated parity drive

RAID 4: It is based on block-level striping with dedicated parity

RAID 5: It is based on block-level striping with distributed parity among the drives. Minimum of 3 disks is required to create RAID 5. If a single drive fails, still it will be functioning.

RAID 6: It is based on block-level striping with double distributed parity thus provides fault tolerance up to two failed drives

Note: Data striping is a practice of saving consecutive segments of logical sequential data on different physical storage devices. disk mirroring is the replication of logical disk volumes onto separate physical hard disks in real time to ensure continuous availability A parity bit, or check bit is a bit added to the end of a string of binary code that indicates whether the number of bits in the string with the value one is even or odd. Parity bits are used as the simplest form of error detecting code.
Among the above RAID implementations, RAID 5 is the popular one.

Which one to choose?

In RAID 5 the data blocks and parity is striped among all disks. Though it offers good data protection, it has few drawbacks too.

  • 20% of the disk space is allocated for parity.
  • If the data blocks are large, the read performance will be slower.
  • When a RAID 5 is to be rebuilt, a lot of complex parity calculations needs to be done for every block. Building the disk from scratch is quite sophisticated and time consuming. If a single sector on the RAID 5 array demise, the whole array needs to be rebuilt. As the size of disk will be more, the time taken for rebuilt will also increase accordingly. Comparatively RAID 6 is treated as a better choice in comparison to RAID 5. 
If even a single disk fails, the whole RAID 5 array becomes erroneous. The problem disk hasn’t been repaired, Meanwhile a second disk demises. In such case, you may lose your important data. In such case the faulty drive needs to be rebuilt while it’s online and in production. If RAID has stopped working properly due to any logical issues, you can have a quick and easy RAID recovery by using the Stellar Phoenix RAID Recovery software. The software can recover raid data from various RAID configurations of RAID 0, 5, 6 and 10 servers.
Using the software, you can recover deleted documents, files, folder, multimedia files and emails from Windows drives, external media, and RAID 0, RAID 5, and RAID 6 arrays. It lets you recover lost/missing RAID logical volumes, FAT, exFAT, and NTFS partitions of size 2 TB or more. You can preview the list of recoverable items before actual recovery.

The software offers 'Remote Recovery' feature to perform recovery over a network or remote location. To build the probable RAID construction, the software automatically matches patterns and parameters of the RAID configuration. If you don’t remember these details, simply select the 'Don't know' option and parameter values (Strip Size, Parity Order, Parity Delay etc.).

If the software fails to build RAID construction then you can perform RAW recovery using virtual RAID construction. Using the tool, you can create image of your problematic hard drive volume or external media and perform recovery from the drive image. Signature based recovery comes handy if the quick recovery fails to recover the lost data. The software let you recover corrupt or incorrectly burnt CD DVD burnt on Windows, Mac, UNIX or Linux. You can benefit the S.M.A.R.T features using the 'Drive Status' option of the tool. This feature let you gather the hard disk information about serial number, model number, size, status, temperature and firmware revision etc.