Hard disk redundancy in Windows and OSX.

The last 18 years I’m a computer user, I faced three times a great loss of data from corrupted disks. In computing there are two kinds of people, those who lost files and those who will loose files. Every hard disk will eventually temporary or permantly fail after three to ten years.

The obvious and easy answer to this problem is making a back up. That process is good but its boring and time consuming. A proper backup should be done continously and incrementally. 


Time machine of OS X is a back up app,  by far better from the windows back up.
Time machine of OS X is a back up app, by far better from the windows back up.
 The time machine application of OS X is a nice solution. Back Up has two disadvantages. First the automatic interval of incremental Back Up can take a day. Second, a complete restore of a failed hard disk can take five hours or even more. 

The best solution is RAID 1 (Redundant Array of Inexpensive Disks). As its acronym indicates, it is an inexpensive solution of data safety. The same data is  written and read in at least two disks at the same time. The probability of both disk failing simultaneously is extremly rare. There are many kinds of RAID types. Initially RAID was based on hardware. A RAID card or an embedded raid controller on the motherboard was needed. Hardware RAID offers speed and reliability. Nevertheless modern operating systems and fast CPUs can emulated RAID without any use of special hardware. 

Windows 7 professional and OS X Lion 10.7 offer software RAID 1 with some limitations. Of course the hardware RAID is the best but software RAID is equally safe.

Windows 7 professional doesn’t use the name RAID 1 for copyright reasons. Instead it uses the mirrored disks name. Mirrored disks can’t be created through USB. From my experiences SATA disks directly connected to the motherboard work fine as mirrored disks. In desktops its easy to add two extra disks and make them mirrored. 

On laptops the case is different. Most laptops have one bay for hard disk and one for the DVD drive.  

Many big laptops have double HDD bays. These are ideal for Raid 1 mirrored disks.
Many big laptops have double HDD bays. These are ideal for Raid 1 mirrored disks.
 Some bigger ones 17″ and 18″ have two bays for HDD. Again this doesn’t help to create mirrored disks. The drive in which the windows 7 professional  operating system  is installed can’t be mirrored afterwards. Althought Windows 7 professional  can be clean installed from the beginning on a ready made two mirrored disks. 

For laptops a DVD caddy bay can help. 

  Removing the DVD drive we replaced it with a caddy DVD drive that accepts a hard disk. That way a typical laptop can at least have two hard disks or even three. 

The way of creating mirror disks is simple under windows 7 professional or Ultimate. (Not all windows 7 versions offered mirrored disks. Windows 7 starter, basic or premium don’t offer that potential).   

Disk Management of Windows 7.
Disk Management of Windows 7.
 Right click the computer icon and select Computer Management. You must have logged in as administrator. then select disk management. Now the first step is to make the hard disks we want to mirror, as dynamic. Second step is to right click and select mirror disk from one of the two disks and from the next window insert the other disk to be mirrored.  

Mirrored disks RAID 1 under windows 7 professional.
Mirrored disks RAID 1 under windows 7 professional.
 That’s all. A new hard disk will appear on My Computer which is actually a bunch of two disks. In case one of the two disk failed the windows will try to fix the problem and notice the user. Otherwise a classical backup will be needed and a replacement disk to be mirrored. One way or another the data won’t be lost. 

On OS X the disk utility app permit the Raid 1 with usb disks.  

 This is very convenient and safe way to expand your data storage. Also theoretically you can clean install an OS X opeeating system on RAID 1 disks. The way of creating a RAID volume on OSX is far easier than in Windows 7 Professional.