The use of RAID 1, also often known as a mirrored array or pair, is a common feature in high end servers where availability is of the utmost importance. This type of RAID uses a pair of hard disk drives, onto which the same data is written to each, hence one drives is a mirror of the other.
Data recovery from a mirrored array are now more common than a decade ago, partly due to their increase use, but also other factors have to be taken into account. Data recovery from a mirrored pair of hard disks is usually only required if both drives have suffered a failure, a scenario which DiskEng have vast experience of.
Safety of Data is Paramount
When the safety of your data is of the utmost importance the use of a RAID 1 mirrored pair of hard disks is a prudent option, as it provides the highest level of data redundancy. The only significant drawback of using a mirrored pair of disks is that it halves the potential capacity and little or no difference in write speeds, despite the both drives being written to. In some cases, the data transfer speed when reading can show a small increase, where the data from the fastest drive to respond is returned to the host.
RAID 1 architecture has become increasingly attractive as the price of storage has tumbled, with some system even utilising a pair of SSD drives. Despite RAID 1 architecture providing a high level of safety for your data, the need for a backup plan should not be ignored, as both disks can fail at the same time either through wear and tear or a disaster.
Re-mirror RAID 1 Drive
When a single disk fails in a RAID 1 array it will remain operation in what is known as degraded mode. It is important that the failed drive is replaced as soon as practicable, in order to re-mirror the data from the working drive onto it.
Even though data transfer speeds have increased by several orders of magnitude, there has also been a comparable increase in hard disk capacity, such that in many cases the time taken to re-mirror the data is significant, during which time the data is vulnerable. It is common to acquire both the drives from the same supplier together, which will most likely come from the same batch and then run in the same operating environment. Due to the way hard disk drives suffer wear and tear over time, there is a high probability that two drives operating within the same conditions will have a very similar lifetime. This means that there is a significant risk of the second original drive failing during the rebuild process and a factor in the increased requirement for data recovery from RAID 1 arrays.
RAID 1 Mirrored Data Recovery
Most total failures of a RAID 1 set occur during the re-mirroring process, but there should be little reason to panic. The most important thing is to make sure that the two original drives using in the RAID 1 disk set are sent to a professional data recovery company, such as DiskEng, in order to recover the files as quickly as possible. It can in some circumstances be beneficial to also send the drive the data was being rebuilt to for data recovery, as it may provide some benefit in the event that the fault on the failed drive was of a serious nature.
If a drive fails and it the RAID 1 array is allowed to run in degraded mode for a significant period of the time, the drive which first failed may end up being of little benefit if a lot of file system changes occurred in the meantime. It is only in the event of ignoring a failed drive or both having the same failed unreadable sector that any data loss is likely to occur.