Failure Types - RAID / NAS

RAID Definition:

RAID (Redundant Array of Inexpensive Disks / Redundant Array of Independent Disks) is where your data, within the RAID Storage, is ( under the control of a RAID Controller ) written across multiple disks with the intention of either:

  • Reducing the impact of individual disk failure on the availability of data storage by mirroring, striping etc.
  • Reducing the impact of unrecoverable read sectors on the availability of data storage by mirroring, striping etc.
  • Increasing overall capacity or performance of storage by combining several disks into one storage container by spanning etc. In this situation capacity is expanded whilst making the storage even more reliant on individual disks.

The most common RAID levels encountered in RAID Data Recovery are:

RAID 0   Spanning / Anti-RAID: RAID Data Recovery required even where an individual hard drive fails.

RAID 1   Mirroring: RAID Data Recovery required here only where the second disk fails the first one already having failed and not being noticed.

RAID 5   Distributed Parity: RAID Data Recovery required where a second disk in the Array fails.

For more information on RAID:

RAID Data Recovery :

Essentially a RAID Array is a collection of physical disks logically bound together by a RAID Controller and presented as a single storage volume to the system ( Computer, Server, DVR etc. ) utilising that storage. This RAID controller has to continually perform some “mathematical magic” in order to achieve this including knowing what sequence to Write To / Read From and how to handle any errors or failures that arise. RAID data recovery generally revolves around these main areas:

  • An intermittently faulty RAID controller can cause write errors to the RAID array itself making the RAID volume unmountable and, consequently, inaccessible.  In most case there are no issues whatsoever with the underlying physical disks and the majority of the stored data thereon is intact. However, in RAID data recovery there is also the liklihood that corrupt information has been written to the disk array ( by the intermittanlty faulty RAID controller ), here, RAID recovery involves a complete, byte-level, analysis of the structure of the data across all the component disks of the array and thoroughly understadming the logical data structure before commencing a complete RAID rebuild from disk images.
  • RAID arrays, as outlined above, are designed to make the whole storage volume less susceptible to individual disk failures. However, this protection often extends to the failure of one disk of the RAID Array only. It can often be the case that an individual disk has failed unnoticed and undealt with. From that point, all immunity of the RAID Array to single disk failure is gone and in the case where a second disk subsequently fails, data recovery is required.
  • RAID configuration on RAID controller lost or overwritten by RAID re-configuration.
  • RAID Rebuild failures. When a failed disk is replaced in a RAID Array that disk has to be “rebuilt” to contain the appropriate data to re-instate full protection

Please Note: RAID Data Recovery Assessments have to be charged on a per-Drive basis as all drives have to assessed in order to establish the recoverability of the whole array.

NAS / Network Attached Storage Definition:

NAS, in general, refers to a device / server whose only function is to allow storage be connected directly to the network. NAS boxes rarely come with a screen, keyboard, mouse etc. and generally are configured via web-inerface. They can come with a variety of operating systems e.g. Linux, Windows etc. However, almost always, the underlying storage technology is generally the same – being, either, single drive, RAID or JBOD ( Just a Bunch of Disks ) implementation.

NAS Data Recovery :

Data recovery from NAS storage is, generally, unaffected by the fact that it is NAS storage but more, rather, by the underlying storage technology e.g. individual disk, JBOD or RAID. There fore data recovery on these systems will follow the data recovery process as those systems.

Please Note: Data Recovery Assessments on Multiple-Drive NAS boxes have to be charged on a per-Drive basis as all drives have to assessed in order to establish the recoverability of the whole NAS.

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