The most common RAIDs require between 2-4 drives.
RAID0 requires a minimum of 2 drives
RAID1 requires a minimum of 2 drives
RAID5 requires a minimum of 3 drives.
RAID10 requires a minimum of 4 drives.
Four disks minimum. http://www.acnc.com/04_01_10.html
The minimum number of harddrives for a fully functional raid 5 system is 4 hard drives.
A minimum of 3 disk drives for Raid-5 volume
Raid level 5 supports reading and writing, but writing performance is slower than raid levels 0 and 1.Raid level 5 requires a minimum of 3 drives.
RAID 1 is mirroring without parity or striping. It requires a minimum number of two drives and has a fault tolerance of one. RAID 1 works by writing data to both drives, thereby producing a mirrored set. When the read is requested, it is serviced by the drive that has the lowest seek time plus rotational latency. An example of this set-up is two 1TB drives in RAID 1 that have a combined total of 2TB of storage, but because they are in RAID 1, the effective storage space is 1TB as data is mirrored on both drives. It is effectively a real-time back-up system. If one drive fails, data is not lost.
There were originally five different RAID levels. However, you can use a number of hard drives to create more raid levels, although this may affect performance.
Sorry, but I disagree with Rtrahan once again. His answer doesn't even appear to apply to the question that is asked.It seems that what the RAID array is telling you is that Disk #4 has failed and needs to be replaced. If you mean to say that your RAID array failed on you completely (such as due to a power outage) and you are wondering which of the drives (if any) are physically damaged, then the only way to determine that is to get into the diagnostics of the RAID array itself. In the diagnostics, it should tell you if any of the drives are degraded or failed. If you have only one such drive, then you can replace it and the array will rebuild itself (which is what it is designed to do, of course). If you have two or more in a degraded state, then I hope you have a backup because all your data is toast unless you want to send the array off to a data recovery lab and pay big bucks to have it restored.RAID 5 arrays must have a minimum of three drives to be set up initially (but can be used with any number of drives that the computer or NAS or other RAID-compatible device can address). This is so that the data is striped across the drives and the equivalent of one drive is used for parity. Thus, in the case of a three-drive RAID 5, the amount of useful data storage is the equivalent of two drives. The same pattern continues as the number of drives increases: the capacity of the array is the total amount of storage of all but one of the drives. All drives in a RAID array must be the same size and ideally the same model.For greater fault tolerance, RAID 6 is sometimes used. In this case, there are the equivalent of two drives with parity. This allows for two drives to fail rather than just one. The disadvantage is that RAID 6 requires a minimum of four drives to be used but can expand to any supportable number of drives beyond that.If you have any questions or would like further assistance, feel free to drop me a line.
Every RAID level stripes data across multiple drives, which improves performance compared to using a single disk -- RAID 0, RAID 1, RAID 1+0, RAID 5, RAID 6, etc.
A group of hard drives assembled into a RAID array is often referred to as, well, a "RAID array" a "RAID stack" or a "RAID cluster."
RAID stands for a redundant array of independent disks. Thus, a group of two or more hard disks comprise a RAID, or array of physically separate drives.
RAID stands for "Redundant Array of Inexpensive/Independent Disks". RAID works by combining two or more hard drives. It can increase performance and/or data redundancy and/or capacity. There are many different RAID types, the most common being RAID 0 (stripe), RAID 1 (mirror) and RAID 5 (stripe with parity).In a RAID 0 (stripe) array, data is split equally between the number of disks in the array. For example, when a 2 MB file is written to a RAID 0 array with two hard drives, the file is split in to two parts and 1 MB of data is written to each hard drive. This increases capacity and performance, but sharply decreases redundancy since only one of the drives needs to fail for all information to be lost.Performance = Drive Speed * Number of DrivesCapacity = Drive Size * Number of DrivesRedundancy allows for no drives to fail.In a RAID 1 (mirror) array, a complete copy is written to each hard drive in the array. Capacity and performance stay the same, but redundancy is increased. As long as one drive works, you will not lose data.Performance = Drive SpeedCapacity = Drive SizeRedundancy allows for all but one drive to fail.In a RAID 5 (stripe with parity) array, you need at least three hard drives. Files are split up to all but one of the drives (similar to RAID 0) and a parity bit is written to the last drive. This increases performance, capacity and redundancy. Performance is not as good as RAID 0, but still better than RAID 1. Redundancy is not as good as RAID 1, but is still quite reliable.Performance = Drive Speed * (Number of Drives - 1) (Theoretical)Capacity = Drive Size * (Number of Drives - 1)Redundancy allows for one drive to fail.There are other RAID levels, but they are not as common.The main benefit of using a RAID array is data redundancy and/or performance.Non-commercial (home) users and enthusiasts wanting a very large increase in performance (theoretically multiples of the number of drives used) usually go for RAID 0 since they often are not too worried about drive failure and they enjoy the larger drive capacities that it provides.Small businesses who only need cheap redundancy usually go for RAID 1. If one drive fails, the drive can be replaced and the mirror array restored.Larger businesses or those needing file/database performance go for RAID 5. They can afford the price of an extra drive and a more expensive RAID controller. RAID 5 provides high performance with large capacities while still maintaining data redundancy and is the most desirable in a business or enterprise environment.There are some other options for RAID such as RAID 10 or RAID 01.RAID 10 features two separate RAID 0 arrays which are then mirrored in a RAID 1 array.RAID 01 is the opposite, with two separate RAID 1 arrays which are then striped with a RAID 0 array.There are other non-standard RAID levels, but most are rather uncommon.Alternatively, there is also drive spanning (aka JBOD), but this provides no extra redundancy or performance. Drives are "glued", if you will, end to end.The benefits of each RAID level vary. The type of RAID used depend on the job it must fulfill.
A RAID 5 uses block -level striping with parity data distributed across all member disks. RAID 5 has achieved popularity due to its low cost of redundancy. This can be seen by comparing the number of drives needed to achieve a given capacity. RAID 1 or RAID 0+1, which yield redundancy, give only s / 2 storage capacity, where s is the sum of the capacities of n drives used. In RAID 5, the yield is . As an example, four 1TB drives can be made into a 2 TB redundant array under RAID 1 or RAID 1+0, but the same four drives can be used to build a 3 TB array under RAID 5. Although RAID 5 is commonly implemented in a disk controller, some with hardware support for parity calculations (hardware RAID cards) and some using the main system processor (motherboard based RAID controllers), it can also be done at the operating system level, e.g., using Windows Dynamic Disks or with mdam in Linux. A minimum of three disks is required for a complete RAID 5 configuration. In some implementations a degraded RAID 5 disk set can be made (three disk set of which only two are online), while mdadm supports a fully-functional (non-degraded) RAID 5 setup with two disks - which function as a slow RAID-1, but can be expanded with further volumes. In the example on the right, a read request for block A1 would be serviced by disk 0. A simultaneous read request for block B1 would have to wait, but a read request for B2 could be serviced concurrently by disk 1.
Raid 1 is mirroring.
It's called a "raid" disk controller. Using a raid controller you can connect 2 or more hard drives in a number of different configurations; one being that the drives are "mirrored".
Type your answer here...Answer Explanation: RAID 1 uses a minimum of two hard disks to mirror data for fault tolerance. Each hard disk contains a complete copy of the data. Disk duplexing improves mirroring because each disk is on a separate controller. If one disk or controller fails in a duplexing RAID 1 array, the other disk can take over immediately to provide fault tolerance.RAID 5, also known as disk stripping with parity, provides fault tolerance by striping the data across a minimum of three and a maximum of 32 disks, and by storing parity information on each disk. This allows the RAID array to recover from a single disk failure.RAID 0, also known as disk striping, is used to increase performance by striping data over a minimum of two and a maximum of 32 disks. RAID 0 provides no fault tolerance.RAID 3, also known as disk stripping with a parity disk, provides fault tolerance by writing data across three or more drives. Because the least number of hard disks is required, RAID 1 will be used instead of RAID 3.
For Raid 5 all the hard drives have to be of the same speed.
Every RAID level stripes data across multiple drives, which improves performance compared to using a single disk. RAID 0, RAID 1, RAID 1+0, RAID 5, RAID 6, etc. all have better performance than a single disk. Other than RAID 0, all other RAID levels provide fault tolerance. RAID 1, RAID 1+0, RAID 5, RAID 6, etc. all have fault tolerance.
It is a combination of RAID 1 and RAID 0. It takes at least four disks for RAID 10. Refer to A+ at Ch. 6 pages 258.