What happens when RAID fails?

What is RAID? Why and when do you need one? What is the most well-known RAID recovery software? Is it possible to recover data from RAID? What are the reasons and consequences of RAID fail? Interested? Keep reading we know the answers.

RAID stands for Redundant Array of Independent (or Inexpensive) Disks. This term describes the system which allows combining several independent disks into one large size storage. Why? Well, today people handle a lot of huge data and sometimes it just seems too crowded for all of them in one place, no matter how large memory we are talking about. So, this is a job for RAID.

All those small hard disks gathered in the array represents array members. There are few ways to combine array, so called RAID levels (RAID 0,1, 0+1, 1E, 5, 5E, 5 with delayed parity, 6,).

Also, each of those levels has special characteristics of:

  • Fault tolerance – capability to survive one or several disk failures
  • Performance – it presents the change in the read and write speed of the whole array in comparison to a single disk
  • The capacity of the array – which is determined by the number of users data which could be written to the array. The capacity of the array depends on the RAID level.

All RAID types are based on three main methods for data storage or combination of these techniques:

  • Striping – the way of splitting the flow of data into blocks of a certain size and writing blocks across the RAID. This way of storage affects the performance
  • Mirroring – a special technique of data storage which allows identical copies of data to be stored on the array member disks simultaneously. This type of storage affects on the fault tolerance and performance.
  • Parity – this technique of data storage combines striping (splitting data into the blocks) and checksum methods.

What RAID implementation to choose, hardware or software?

We bring you some facts you should know about both solutions.

Hardware RAID has two solutions, inexpensive one – RAID chip, which can be built into the motherboard, and more expensive solution with a complex standalone RAID controller. The advance of this expensive solution is equipment which could include its own CPU, battery-backed up cache memory and hot – swapping support.

A few advantages that hardware RAID has over the software RAID maybe will help you to decide which one you really need. For example, it doesn’t use CPU of the host computer and user can create boot partitions. Communication with the device is directly so it can handle errors better, which, you have to admit, is great and it supports hot swapping.

What about software implementation?

If you have home edition of Windows you will be able to install only RAID 0, while, for example, RAID 1 and 5 are created for Windows server edition. Unlike the hardware RAID, the software implementation in most cases doesn’t implement the hot swapping. Also, it uses CPU of the host computer. It is useful to know that some limitations exist when it comes to system boot which is possible only in RAID software.

Why and when do you need RAID?

RAID is still mostly used in companies with large servers which need access to their critical data 24/7. One of the advantages surely is the simple usage of data in the array.

Although, RAID is also used among private users who want to avoid monthly fees this way and who has some kind of mistrust when it comes to cloud storage services. The most common users are multimedia editors and computer-aided design (CAD) users because they appreciate RAID advantages like high fault tolerance and fast transfer rates. We shouldn’t forget to mention computer gamers here, who also appreciate RAID’s setups.

It is important to know that RAID is not a substitute for regularly backup. True, it can protect against disk failure in some way, but it is not a protection against administrator errors or the one caused by bugs in programming.

RAID fails too – reasons and consequences

When you are faced with hard drive failure it is very important to stay calm. You shouldn’t take any reckless reaction. Although RAID is considered to be a safe system, it can collapse too, even more, that is not so unusual situation.

Users often get panic because they don’t expect RAID to fail. According to the experience of one of the companies that solve this kind of situations, the manufacturer’s support advise you to delete the RAID configuration and try to recreate it. Well, do not do that in any case. It can cause you a permanent damage.

What you should o do when you suspect on RAID failure:

  • If you can hear any unusual mechanical noise from the drive, turn it off promptly – this is one of the situations when we recommend you to call a specialist.
  • Do not run volume repair or defragmenter utilities on suspected bad drives
  • Do not try to replace a failed drive with the one from another RAID system
  • Mark the drives on their position in a RAID array

Three general RAID failure reasons

  • One of the RAID member disks failed
  • Several RAID member disks failed
  • Other failures that are not related to member disks. It can be controller failure or operator error.

Is it possible to recover data when RAID fails?

When it comes to RAID failure there are some rules you should follow. For start, when you realized you are facing the RAID failure, you need RAID recovery. The first step is to write down everything you know about original array configuration.

In a hardware configuration, it means you have to mark all the member disks along with controller ports and cables.

On the other hand, you have logical RAID configuration which refers to RAID type, disk order, a number of member disks, block size, start offset for the data on the member disks (if this information is available).

If you want to return to the original configuration, you have to collect all the above-mentioned information.

How to prepare member disk for recovery and what you will need?

  • Disconnect disk from a controller
  • Don’t try to rebuild an array using the same or another controller if you don’t know correct the RAID parameters.
  • Always create the disk image files from separate disks instead from entire array. The thing is that some parts are inaccessible unless you disassemble the array.

After you detected all parameters you have two possibilities to move on with RAID recovery process. In case you need all RAID’s content write somewhere a copy of the RAID and if you need just some files, you should use regular data recovery program.

The most common problems when it comes to RAID recovery are the capacity of data and sizes of the array. It is important to consider a configuration which is able to fulfill all resources needed in terms of speed and capacity. Sometimes you will need free disk space same size as files you want to recover, and sometimes situation could be more serious and demanded a two or three times more disk space to store simultaneously original disk images and recovered files.

5 most well-known RAID recovery softwar

  1. ReclaiMe Free RAID Recovery ( http://www.freeraidrecovery.com/)This is very simple to use software which doesn’t require special technical skills. It works with most common RAID types (RAID 0, RAID 5 and RAID 10). ReclaiMe RAID recovery doesn’t work with the single hard drive and there is no way to recover file by file, it can only handle array as one whole. Support Windows.
  2. Diskinternals (http://www.diskinternals.com/raid-recovery/)DiskInternals is a software which allows switching between automatic and manual modes. Also, it has the possibility to detects the type of the disk array automatically. Supports Windows.
  3. Runtime (https://www.runtime.org/raid-recovery-windows.htm)It provides recovery for NTFS-formatted Windows RAIDs and includes hardware RAIDs and Windows software RAIDs. Runtime is easy to use software, fully automated and runs from the Runtime Live CD https://www.runtime.org/data-recovery-live-cd.htm and WinPE boot CD-ROM ( https://www.runtime.org/peb.htm). Supports Windows.
  4. ZAR – Zero Assumption Recovery (http://www.z-a-recovery.com/)Powerfull software that works with RAID 0 and RAID 5. It runs only on Windows and Linux, doesn’t cover Mac.
  5. R-Studio Data Recovery Software (http://www.r-studio.com/)This is a collection of software which uses advanced techniques in data recovery. It works with RAID 0, RAID 5, RAID 4, RAID 6. Runs on Windows, Linux, and Mac.