All modern motherboards are equipped with an integrated RAID controller, and more progressive models even have multiple build-in RAID controllers. However, not every desktop user knows how to build a RAID array, what array level to choose, and he or she doesn’t clearly understand the pros and cons of using RAID arrays.
So, RAID stands for Redundant Arrays of Independent Disks. Fault-tolerance is achieved by data redundancy. The improvement of the RAID system performance is provided by the simultaneous running of several disks. In this sense, the more drives in the array (up to a certain limit), the better.
RAID levels
Currently, there are several RAID-levels, which can be considered as standardized – RAID 0, RAID 1, RAID 5 и RAID 6.
Different combinations of RAID levels are also used, which allows you to combine the advantages of different RAID levels. Usually, this is a combination of a fault-tolerant RAID level and RAID0, applied for increasing the performance (RAID 1+0, RAID 50).
Also, all modern RAID-controllers support JBOD (Just a Bench Of Disks). It provides the ability to connect individual disks to a RAID controller.
Pay attention that RAID controllers, which are integrated into motherboards of desktop PCs, don’t support all RAID levels. 2-SAS Ports RAID-controllers support only RAID0 and RAID1 levels, but RAID-controllers with many SAS Ports also support RAID10, RAID5, or RAID6 levels.
RAID 0
RAID 0 isn’t a redundant array, and of course, it doesn’t provide reliability for storing data. However, this RAID level is widely used in cases when it’s necessary to provide high performance of a disk subsystem. When creating a RAID 0, the data is divided into blocks (also they are called stripes), which are written to separate disks, so the system with parallel access is created. Due to the ability of simultaneous read/write operations from multiple disks, RAID 0 provides maximum data transfer speed and maximum disk space usage because it doesn’t require space for storing checksums.
The implementation of this level is very simple. Generally, RAID 0 is used if the fast data transfer is required.
RAID 1 (Mirrored disk)
RAID 1 – is an array of two disks with 100% redundancy. In other words, the data is completely duplicated (mirrored) due to what the very high level of redundancy is achieved. Such RAID level is used mainly in cases when the cost of data safety is much higher than the cost of implementing a storage system.
RAID 5
RAID 5 – is a fault-tolerance disk array with data checksumming. When writing, the data is divided into blocks and simultaneously written to all drives in the array in a particular pattern. In each row, one of the disks stores a certain checksum, the so-called parity function, which is calculated based on the data from other member disks in the row.
In the case of RAID 5, all disks in the array have the same size, but the size of storage available for user data is reduced by one disk. For example, if you use three disks with a size of 500 GB, the actual size of the array is 1 TB (not 1.5 TB) because 500 GB is allocated to store parity data.
RAID system reliability
Like all devices in the world, RAID arrays can fail. The main reasons for failure are:
- Disk failure
- controller failure
Disk failure
If there is a disk failure in the RAID 0 array, unfortunately, the data is lost forever.
|In the case of RAID 1, the disk failure isn’t dangerous because the absolutely identical copies are stored on the disks.
Also, the disk failure doesn’t lead to the loss of user data in RAID 5. Just replace the failed drive, and the controller rebuilds a RAID.
Controller failure
If the controller fails, the situation is more difficult. In this case, you have a set of healthy disks, but it’s impossible to access them. If you, for example, buy a new controller and connect the drives to it, then most likely, the new controller won’t detect the old RAID configuration and initiates a RAID rebuild. If you do this, the data will be totally lost.
In case of a failed controller, the best (but also the longest) solution is to recover the array configuration using a free tool – ReclaiMe Free RAID recovery.
Conclusion
For home users, RAID0 and RAID1are the most popular solution. Using RAID arrays consisting of three and more disks in a desktop PC is rather the exception. The reason is that, on the one hand, the cost of the RAID array increases in proportion to the number of disks involved. On the other hand, the capacity of a disk array is more important for home users than the performance and reliability.