Survive a Hard Disk Failure by Using RAID 1

I’ve met a lot of paranoid people during my time working with them and their computers. This is especially true where hard disks are concerned. Yet, the fault can’t all be put on them. However, many users still don’t understand that computers, especially hard drives, can and will malfunction at one point or another and when that happens, all of their data will disappear. There are definitely a lot of different ways to back up your precious data. Many of them consist of using backup software so that you can either manually back up your data or define a schedule and have it done automatically for you. However, one major factor can have a big impact on your computer and data: the physical hard disk itself. If you are worried about a hard disk malfunctioning and have the need to be back up and running in as little time as required, then a RAID 1 array is just what the doctor ordered!

For Windows 8 users, rather than using traditional RAID technology as shown in this article, you have the option of using Microsoft’s newest offering where disk storage and redundancy is concerned, Storage Spaces. The concept works very similarly to RAID. I’ve talked about Storage Spaces exclusively on a specific blog post, which you can find here.

What is a RAID 1 Mirror?

When it comes to the physical hard disks within your computer, there is a technology called RAID (Redundant Array of Independent/Inexpensive Disks) that allows you to pool one or more hard disks together so that more can be achieved from them than if those hard disks were left alone to each work by itself. With RAID technology, you usually get to achieve two different goals: faster speed and more redundancy or reliability to your data. With RAID, there are also many different levels that allow you to achieve a mixture of speed and/or redundancy. The most popular implementations of RAID include RAID levels 0, 1 and 5. The more popular choice where home users and a need for redundancy are concerned is RAID 1, also called mirroring.

If you had one hard drive full of important data, wouldn’t you agree that one of the most efficient ways to backup those data should that hard disk fail is to make a copy of those original data and write them onto another physical hard disk? In other words, doesn’t it make sense to make a near 1:1 copy of that data elsewhere? If what I just said makes a lot of sense to you, then you just basically understood what RAID 1 is all about! I’ve always tried my best to teach users that backing up data does not have to be complicated at all. Heck, you could easily just do a copy of your important data, paste it onto your removable USB thumb drive and call it a day. You end up with a backup copy on the thumb drive so that if something disastrous happened to the original copy, you’d still be saved. However, I doubt you’d want to manually copy and paste data files back and forth each and every time you’ve created or modified a file. That is where a RAID 1 mirror comes into play.

As its name suggests, a RAID 1 “mirrors” every single piece of data you have on one hard disk and duplicates it onto a second physical hard disk automatically. This means that if you have 10,000 files on disk 1, you’d have the exact same 10,000 files on the mirrored drive, disk 2. If you erase 5,000 files from disk 1, then those same 5,000 files will also be erased from disk 2. This makes disk 2 an exact mirror of disk 1. All of this happens without you ever having to initiate any sort of backup software or waiting for a specific backup schedule to kick in.

RAID 1 Diagram

Advantages and Disadvantages

As with all things in life, noting is perfect and implementing a RAID 1 mirror is no exception. You need to understand what RAID 1 can and cannot do for you prior to you relying on it:

Easy setup – Setting up a RAID 1 mirror within Windows is extremely easy. I mean it. It just takes a couple of mouse clicks!

Automatic – Once configured, Windows will take care of everything for you. From then on, every existing, newly created and modified files will be automatically mirrored to the other disk all without you having to do anything.

Minimize downtime – RAID 1 minimizes downtime from a hard disk failure. If your original drive suffers a hardware malfunction for any reason, you can quickly get your system back up and running by booting to the mirrored disk (assuming your mirrored the system drive and not a data only drive).

50% Overhead – By implementing a RAID 1, you are essentially paying a 50% penalty. For example, if the original hard drive that you want to mirror is 500GB in size, then your mirrored disk will have to be equal to or larger in size as well. Essentially, you are using 1TB of storage space to store 500GB of data, hence the 50% penalty.

Not real “backup” – I think this is debatable as it really depends on how you work with your data and computer in general. Many users don’t consider a RAID 1 implementation as a substitute for a real backup solution due to some of the following reasons:

  1. Because both your original and mirrored disk are most likely inside your computer, a natural disaster such as a house fire have a good chance of destroying both hard disks. If a burglar physically steals your computer tower, then both physical disks are lost to you as well.
  2. A RAID 1 mirror doesn’t provide any “point in time” copies of your data like how a real backup software does. If you’ve mistakenly overwritten a important document, that erratic change will also be reflected on your mirrored disk. RAID 1 doesn’t know the change you’ve just made was unwanted nor does it actually care. All it does is mirror everything you do one the primary disk onto the secondary.
  3. Viruses and malware that infects your original drive will also be “mirrored” onto the other disk. If the malware renders your documents useless, your mirrored disk will reflect this change as well.
This topic on whether a RAID 1 can be considered a true backup solution can be debatable. Again, this all depends on what risks you are willing to take and whether they are acceptable to you or not. Not having a data backup in an offsite location is not acceptable to some but perfectly warranted for others. My advice once again is that prior to implementing a RAID 1 solution, think about whether or not  it fits your computer usage style or not.

Portability – If you plan on moving disks in a RAID 1 mirror to another computer, things can get complicated very quickly. If you are not experienced in RAID technology, just “pretend” that moving disks from a RAID 1 array to a different system cannot be accomplished. This will save you a headache for now. If you do wish to perform this feat, which is definitely possible, then you should take a look at using a hardware based RAID solution rather than a software based RAID as what I will be showing you here.

Computer crash – If your computer will not boot at all and it’s not due to a an issue with your hard disks, then you will be left completely in the dark. Although you might have a working laptop or secondary computer, you won’t be able to access your data on the RAID 1 array (assuming no online backup of the data you need to work with exists) without extra work such as physically removing one or both of those disks and getting it to work on that secondary computer which once again brings up the portability problem above.

As you can see, there are definitely a lot of think about prior to implementing RAID 1. Although this technology is mainly used in business environments, they usually have some other type of true backup system in place as well. Using RAID 1 for them in this situation is just to minimize downtime. For home users, there is much less incentive in creating a RAID 1 array in anything but the most specific of scenarios. If having read all this and you are still interested though, then read on!

Creating a Software RAID 1 Array in Windows

I am demonstrating this in Windows 8 but the steps should be equally similar under Windows 7 as well.

The first thing to do is install a second physical hard disk in your computer system. Remember, this mirrored disk will need to be equal or larger in size than the drive you are going to be mirroring from. Once booted into Windows, head over to Disk Management and you should see a pop up window asking you to initialize your new disk. Hitting OK should be fine in most cases. In this simple demo, I will simply be mirroring my system drive. For home users, this is the most likely scenario as well.

Initialize Disk

Disk Setup

To create a mirror of my system drive, Disk 0, I simply right-click on the first partition on Disk 0 and select “Add Mirror”.

I’m not quite sure why I wasn’t able to right click on the Disk 0 option instead to mirror the entire disk in one step. I was only able to mirror individual volumes one at a time on the primary disk. Converting my original and mirrored disk to the dynamic type prior to adding the mirror still didn’t give me the option to select “Add Mirror” on the entire Disk 0. Strange.

Add Mirror

On the next screen, I need to choose which disk will be the mirror. As I only have one extra and empty disk, I will select that one (Disk 1).

Choose Mirror

You might then be presented with a notification pop up window. This is letting you know that it will convert your basic disks to dynamic disks. As basic disk type can’t be used for RAID, they must be converted to dynamic type disks.

Convert Dynamic

Once you hit Yes, the process will commence. Once the first partition has completed its sync process, I then proceed to mirror my main C: partition and repeat the process:

Resynching

Once the resynching process has completed for the second volume, I will then have a perfectly mirrored disk!

Breaking and Removing the Mirror

Once the mirror is configured and completely synced with each other, everything now happens transparently and after a couple of days (or hours), you’ll  most likely forget that the mirror was actually there! However, there are times when you want to break or remove the mirror. For example, if you decide that the mirror is no longer needed and that you’d much rather use the secondary hard disk for a different purpose, then you’ll want to break/remove the mirror. Breaking and removing a mirror are two different things.

Breaking a mirror

When you have a perfectly working mirrored set but no longer have a need for it, you can either break or remove the mirror. The main difference between breaking and removing a mirror is that the former does not erase and reformat the secondary disk after the mirror configuration has been deleted. All of your mirrored data will still reside on it and you can then physically remove the disk out from your system. To break a mirror, simply right-click on the secondary disk within the mirror set and select “Break Mirrored Volume”. Of course, you then receive a warning about doing so will break the data redundancy.

However, if you are trying to break a system mirror, you’ll receive an error message stating that the mirror is the current system or boot plex. It seems you’re stuck at a dead end since the mirror is still active and ongoing. According to Microsoft, this is by design and the correct way to break a system mirror is by using the Diskpart.exe command line utility as followed by that KB article I’ve linked to.

Break Error

Here are the commands I used to successfully break the mirror:

Break Disk

I had to perform that procedure twice, first for the C: volume and the second for the system reserved partition, volume 2. You can see the results below where the mirror is clearly broken but the data is still preserved on my secondary disk. Windows will automatically assign the next available drive letters to the volumes on the mirrored disk. If I now head into Computer, I will see both the C: and E: volumes along with F:. Both C: and E: contains the exact same set of files as each other. However, because the mirror configuration is now broken, any data I add or modify from then on to C: will not be duplicated to E:.

Break Results

Removing a mirror

Fortunately, removing a mirror is much more easier than breaking a mirror because it’s much more destructive! Remember that when you remove a mirror, all data on the secondary disk will be destroyed! In most cases, you will need to remove a mirror once one of the disks within the mirror set fails completely. Because Windows will not be able to connect to the failed disk, you will not have the opportunity to “peacefully” break the mirror. A remove operation is needed. To do so, simply right-click a disk within the mirror and select “Remove Mirror”. You then need to specify which actual disk you want to remove the mirror from and confirm your selections. Once they have been removed, you can see that my secondary disk has been reformatted:

Remove Results

Booting to the Mirrored Disk

Finally, let’s see what happens when our primary disk fails. If all goes accordingly, booting to the secondary mirror is a piece of cake. Why? Because when you created the mirror, Windows knew that you were creating a mirror of the system/boot drive. It then automatically added an entry for you in the boot manager to boot from the secondary disk should it not detect the primary during startup! To simulate a disk failure, I’m just going to disconnect the primary disk.

First, Windows will immediately notice that something has gone wrong and kindly state that we need to perform some sort of recovery as seen below. If you look way down below, you’ll see an option to use/boot into a different operating system. That is exactly what we need to do because remember, the secondary mirrored disk is an exact clone of the original and so there really isn’t a reason why we can’t boot to it. In fact, that’s one of the main benefits of creating a RAID 1 mirror of your system drive in the first place!

Recovery

As I mentioned a bit earlier, Windows automatically wrote a new entry to the boot manager at the time we created our mirror so that we can boot to the mirrored disk. You can see the results here as I can now simply choose to boot to the secondary plex. That’s just a fancy word for the secondary mirror so don’t be too alarmed.

Secondary Plex

Once I have made my selection, as expected, I will be right back inside my Windows system with hardly any changes at all. At this point, Disk Management will also realize something is wrong with our mirror setup and it will reflect as such:

Failed Redundancy

At this point, you either have the option of reconnecting the failed hard disk back to the system (assuming it has been fixed) or in most likely hood, remove the mirror and start from scratch. Remember, you can’t really break the mirror at this point because that can be achieved only when the mirror is in a healthy state. Also, “removing” the mirror can also be misleading because as I said earlier, removing it will cause all data on the disk to be erased. But the failed disk is not connected to the system so how can this be?! Well, this again is misleading. The data on the failed hard disk technically still resides on the disk, assuming you have a method of getting to it such as accessing it via a Live Ubuntu DVD. But this is not necessary because you are now using your mirrored disk, which up to the point your primary disk failed, contains the exact set of data and files. Therefore, you really don’t need the failed hard disk anymore.

It’s still equally important to understand that just because you think the hard disk has physically failed doesn’t automatically mean that data on that disk are unreadable. In fact, it would be a grave mistake if you just threw out that failed hard disk onto the streets!

If you want to re-mirror your now primary disk, you simply repeat the steps by configuring a new mirror for it. Of course, you will need to purchase a new physical hard disk for this to happen!

In the End…

You should now have some good idea of where a RAID 1 fits in your computing lifestyle, if at all. Again, I’d like to admit that implementing a RAID 1 solution for home users is only appropriate in the most specific of scenarios. In most cases, this is the fear or paranoia of a physical hard disk going bad. If the thought of having to completely reinstall an operating system and taking the time to migrate data over from a backup elsewhere is daunting to you, then a RAID 1 mirror might just be for you. Think of it as an always up-to-date “clone” of your primary hard drive. With software image backup solutions, you get to create a full system image backup of your computer, which is great. However, your data is constantly changing and revolving and this image that you create initially quickly becomes outdated unless a new image is created every so often or you implement a different backup strategy in addition to the image backup. With a RAID 1 mirror array, your secondary disk is exactly the same as your primary at all times. No intervention on your part is necessary besides the initial setup and configuration.

But it would be ill advised to treat a RAID 1 mirror as your only and sole backup solution scheme unless you are absolutely sure of what the risks entails from doing so. However, if you create a supplementary backup scheme to go along with it, RAID 1 will start to look much more promising, especially if you have the requirement of getting back up and working on your system as quickly as possible after a single physical hard disk failure!

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Comments

  1. Sorry for late reply so I’m already guessing you have already found the answer. But basically, when your first HD dies and you revert to the second mirrored drive, since we are doing software RAID within Windows, it will notify you in Disk Management that something is wrong with your RAID setup as depicted in my screenshots. What you would do next is to break the RAID setup and that is how you revert back to “raid-less” mode. If you want to mirror again once you have bought another drive, then you’d start over again by creating the RAID 1 mirror and letting the data sync.

    At this point, after booting to the secondary drive and “breaking” the Raid 1. I install a replacement drive and set up a new mirror. Do I need to move the secondary drive physically to the same sata port the primary hdd was on? Also it seems from my testing that replacing the primary hdd and remaking the new mirror from the secondary does weird things to my boot manager. The original windows installation becomes inaccessable and it creates multiple Plex’s. This seems less than ideal. Ideally there would be the main windows boot option with a secondary plex. When replacing the primary drive and creating a new mirror, windows should then know and be able to boot from the windows 7 default OS and only maintain 1 secondary plex. Please let me know if this can be done. Hopefully this all makes sense to you. I typed it out in a hurry.

  2. In the event of the first disk failing (the one holding the original operating system and main boot drive), do you need a recovery disk to start up the second disk?

    Let’s assume that the first disk is now removed from the case, the second disk is still in the same slot/port, and we are able start up the computer with your guide. How do we break the raid 1 in order to revert it to a single drive (a.k.a. the second disk) without having another (a third) hard drive inserted to repair the raid?

    My concern here is that, as you stated, breaking the drive, all after the system is booted and the above assumption is in place, is misleading because the drive is no longer there. Could you clarify which drive I’m supposed to break out in this situation?

    Thanks.

    • Hey Adam,

      Sorry for late reply so I’m already guessing you have already found the answer. But basically, when your first HD dies and you revert to the second mirrored drive, since we are doing software RAID within Windows, it will notify you in Disk Management that something is wrong with your RAID setup as depicted in my screenshots. What you would do next is to break the RAID setup and that is how you revert back to “raid-less” mode. If you want to mirror again once you have bought another drive, then you’d start over again by creating the RAID 1 mirror and letting the data sync.

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