A single drive failure will not result in data loss. Speed and size is limited by the slowest and smallest disk. Only one drive is needed for recovery. RAID 3 Striped set with dedicated parity Data is split evenly between two or more disks, plus a dedicated drive for parity storage. Poor performance for multiple simultaneous instructions.
A single drive failure will rebuild. Parity is split between disks. Large size, fast speed, and redundancy. The total array size is reduced by parity. No parity. Only one drive in a mirrored set can fail. As a result, both read and write performance are severely affected while a RAID 5 array is in a degraded state. RAID 5 is ideal when space and cost are more important than performance. A minimum of four drives is required. RAID 6 becomes attractive when space and cost are important and sustaining multiple drive failures is required.
Read and write performance is increased, but only half of the total space is available for data storage. Four or more drives are required making the cost relatively high, but the performance is great while providing fault tolerance at the same time. In fact, a RAID 10 can sustain multiple drive failures—provided the failures are not within the same subgroup. Performance does not degrade as much as in a RAID 5 array because a single failure only affects one array. Up to four drive failures can be overcome if each failed drive occurs in a different RAID 5 array.
A RAID set offers redundancy and can withstand the loss of up to two disks in each parity set. But when more than two disks in a single parity set are lost, the RAID 0 set breaks, and data recovery is needed. In addition, some of the listed capacity is used for formatting and other functions and will not be available for data storage.
Quantitative usage examples for various applications are for illustrative purposes. Actual quantities will vary based on various factors, including file size, file format, features, and application software. Actual data rates may vary depending on operating environment and other factors. Seagate reserves the right to change, without notice, product offerings or specifications.
All rights reserved. If you have two 1 TB disks, your array size will be 2 TB. This is a common setup in high end desktop systems, since speed matters more than redundancy. Similarly to RAID 0, it uses two or more disks, but rather than striping data across them, the data is mirrored from the first drive to the second and any additional drives in the array. If you have two drives, one of them will be used entirely as a sort of real-time backup, halving your total storage capacity in the process.
If either drive kicks the bucket, you can continue reading from the other drive, and rebuild the array by replacing the faulty drive.
Write performance will be limited to the speed of the slowest drive. However, the redundancy in a server setting is worth much more than the price of a single drive. If you just need a basic drive setup, go with a simple RAID 1 array. RAID 5 is where things start to get interesting.
Parity is a form of error checking, like a hash, but much simpler. Basically, say you have 7 bits of data that you want to send to someone, and you want to ensure that it gets there entirely intact. The solution is to count up all of the positive bits; If there is an even number of ones, the parity will be 0.
If there is an odd number of ones, the parity will be 1. Instead of storing copies of the data which would be like sending a message twice , RAID 5 simply stores a parity bit.
You can imagine it like RAID 0 with redundancy—it requires a minimum of three drives. All but one of the drives are used like a regular RAID 0 array, but the last drive is used for parity.
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