Why do you need RAID 1 and how to recover data when it fails?

What is RAID 1? Why do we need it and when do we use it? What causes RAID 1 failure, and can we recover data when that happens? We bring you below answers to those questions and many other useful facts you should know about this RAID array.

What is the base for RAID 1?

It is based on mirroring – storage technique which allows identical copies of data to be stored on the different array member disks at the same time. This affects the fault tolerance and performance. RAID 1 consists of at least two hard disks where the smallest member disks determine the capacity of the array.

We also know this array as mirrored volume, because data stored on one hard drive will be mirrored to other hard drives in RAID 1 array. This is an advantage in the case when one drive fails. How is that possible? We already mention that the capacity of RAID 1 array is big as the smallest hard drive because the rest of the hard drives are regarded as a mirror. So, we have a situation where the data stored on RAID 1 array is actually stored on one hard drive and mirrored to the rest of the hard drives simultaneously. That gives you a chance to restore data from mirror volume in case of hard drive failure. RAID is a great choice if you need a fast and reliable way for your data protection. It is actually sad to be the most reliable way you could find for online data protection.

Two main variations

We will present you here two variations of RAID 1 – RAID 0+1 and RAID 1+0

RAID 0+1presents combination of striping and mirroring techniques which is the best way to gather RAID 0 performance and RAID 1 fault tolerance. Using a simple mirroring operation it is easy to create RAID 0+1 from the existing RAID 0. For this version, you will need a minimum of four disks because two disks are needed to create RAID 0 which is mirrored on the other array members. What array capacity you could expect here? It is simply determined by the smallest member disk multiplied by the number of the disks in the original RAID 0 version. Because of the fact that half of the array capacity is used for the redundancy, we can say that this is quite an expensive option of RAID per gigabyte storage.

RAID1+0 is a combination of RAID 1 and RAID 0 with all the characteristics of RAID 0+1. It also uses mirroring and striping techniques. In RAID 1+0, allocated disks are mirrored in pairs, and then those pairs are striped.

Even if it sounds similar for the first sight, there are some serious technical differences. The bottom line is that 1+0 is better than 0+1. The difference lies in fact that is hardly possible to create
RAID 1+0 from RAID 1 on-the-fly, because of the complete restriping.

What makes RAID 1 popular?

This solution provides writing two copies of the data at the same time on two different drives. It is called fault tolerance.

RAID 1 usually writes two copies of the data at the same time on two different drives. This is called fault tolerance. If one of the disks fails (suffers a mechanical failure or doesn’t respond), the remaining drives will function and data can be fully recovered using the other disk. 100% redundancy could improve read speed, but what happens with the write speed? If you have two-drive RAID 1, every time when you write data to the drive, a copy is written to the other drive. That means that all changes you made, have to be made twice, so the result is decreased write speed which is main disadvantage of this array.

The RAID 1 configuration could be performed by a software or hardware RAID controller.

Who needs RAID 1?

The purpose of this RAID array is suitable for accounting and other financial data, small database systems, individual users who are looking for fault tolerance, enterprise servers etc. It is extra useful because duplicated set of data is surely more secure than using parity.
Is there a way to restore data when RAID 1 fails? Of course, there is a way.
There are three reasons for losing data from RAID 1:

  • RAID 1 disk rebuild
  • RAID 1 disk failure
  • Formatting RAID 1

Now, when you are familiar with the reasons for losing data, you probably ask yourself what kinds of situations could lead to those three reasons.
Three ways that can cause data loss:

Data loss caused by human mistake

We all make mistakes for a number of reasons. Sometimes you are in a hurry, sometimes it is because of lack of concentration, stress or any other factor. The point is, that can happen to everyone and when it happen, panic is probably the first reaction. But it shouldn’t be, because if the human factor is “guilty” for data loss from RAID 1, those files can be recovered if data is not overwritten.

What are possible scenarios:

  • Mistakenly press Shift+Delete, or you delete accidentally data from Recycle bin
  • Accidentally cause disk drive formatting
  • Some other mistakes like lost files after cutting them from one drive to another

Data loss caused by RAID 1 array failure

If just one drive in the array is being corrupted, you can recover data from another hard drive due to data redundancy. On the other hand, if both drives are damaged, the best solution is to leave the data recovery to the professionals. In case of RAID 1 array failure you can expect the following messages:

  • RAID 1 drive is not readable or recognized
  • File system of RAID 1 drive turns to RAW format
  • Disk drive is not formatted do you want to format it now?

Data loss caused by hard drive physical damag

Physical damage means that disk is damaged by water, fire or it is just broken into several pieces. If this happens it is unable to recover files because the system can’t recognize the drive.

Software that could help

In the end, we suggest you a few recovery software which supports RAID 1 array:

iCare Recovery http://www.icare-recovery.com/howto/raid-1-file-recovery.html
EaseUS http://www.easeus.com/data-recovery/other-recovery-software/free-raid1-recovery-software.htm
ReclaiMe http://www.reclaime.com/
Diskinternals http://www.diskinternals.com/raid-recovery

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