It will withstand a disk failure. But it won't withstand loss due to deletion, corruption, ransomware or a rebuild on a member with its own problem, as the “damage” occurs simultaneously to each disk in the RAID mirror.
When one disk can't read an address, often the second member can. In this case the work is merging the images of the two disks to create one total image, not building onto a new replacement as the original survivor continues to be under load.
RAID 1 mirrors. When you write anything to an array on a RAID 1 setup, every write will go to both disks. This means each disk has a complete (and completely independent) readable copy of your whole volume. That makes RAID 1 the most recoverable setup in common use, and the one most likely to be resolved without any specialist work at all.
Typically, you're going to find that when you lose a RAID 1 set, one disk is fine. A RAID 1 mirror does not contain files or data in some “proprietary” manner; it's the actual filesystem (complete with a small amount of controller-specific metadata at one end). So if you take this working disk and connect it to a normal computer (i.e., outside of your failed RAID), you can frequently mount it and read its contents directly.
You might want to try this before paying someone. We'll tell you that over the phone.
Both disks failed, at different times. This is the most common case. For example, one disk has been dead for months without anyone noticing, and the RAID has run unprotected for those same months until the second disk died. Once both disks are imaged, the better of the two images is used to restore the lost data. Wherever that image has holes, those areas are filled with whatever exists on the other image.
The mirror was silently broken. At some point, one disk dropped out of sync with the other. When this happens, no alarm occurs and you now have a mirror of older data, several months old. You can recover the data, albeit potentially as an outdated version rather than the current one.
Corruption was mirrored faithfully. RAID 1 simply copies whatever is fed into it. Therefore, ransomware attacks, deletions and file system damage will all replicate perfectly onto each side of a RAID 1 configuration. That's why redundancy isn't backup.
A rebuild was started onto a good disk. If rebuilding starts in the wrong direction, then the remaining good data will be overwritten by the bad data from the failed drive. What would normally be a simple recovery process becomes much harder, and this happens more than it should.
Remove one of the drives from the RAID array and attach it directly to a computer via either a SATA port or a USB adapter. The member of a hardware RAID 1 often mounts as simply another normal volume because the “mirror” is simply the file system plus some additional metadata.
If it mounts, copy all of your data off right away. Do not place it back into the RAID array and do not start a rebuild until you have copied your data elsewhere.
When mounting fails to occur, stop there. Do not initialise it, do not allow Windows to format it, and do not attempt to do the same for the second drive before the first is imaged.
Until this is replaced, you are unprotected. It is during the rebuild operation that you are at the greatest risk. Copy your data from the working drive prior to starting the rebuild, not after.
Frequently, yes, on hardware RAID 1. Each drive contains the full filesystem. If you can mount the drive, make sure to extract all data from it prior to taking any further action.
Typically can be recovered. When the two fail, it's usually not together. So, there will typically be one that is in significantly better shape than the other. Both disks are imaged, and the better of the two is then selected to serve as the base.
It seems worse than it actually is, depending on how far the rebuild got. Stop the rebuild process immediately and send both drives as soon as possible. Do not restart the rebuild.
No. A RAID writes whatever happens on both disks. So, any damage that is written to one disk will also be written to the other. RAID only provides protection against a disk failure. It does not protect against any other type of loss, and it is not a backup.
Costs start from £500 +VAT for array-specific recovery. However, where one member of the RAID reads and you need to pull only that particular data from it, with no further array-specific work required, we may quote this as single-drive recovery from £300 +VAT instead.