Rebuilding reads all the data from the remaining disks, calculates the lost data, and writes the recovered data back to disk. Rebuilding a RAID array takes time and a significant amount of processing power. That means A2 can be computed using A1, A2 and A p. Its contents are such that all the data blocks plus the parity block equal zero when XOR'ed together. It can be recovered in a process called rebuilding, where the RAID array is fixed using the parity block. Let's say that disk 1 fails, meaning that A2 is lost. So how does parity help with fault tolerance? If we look at the diagram above, we see that the data labeled A is split into 3 parts plus a parity, A p. Therefore the minimum number of drives is 2 + 1 - two drives for the actual data and one for the parity. However, to make it more fault-tolerant than RAID 0, a particular block of data called a parity block is, effectively, written to an extra disk. Other RAID levels offer excellent reliability at less cost.ĭiagram showing RAID 5 configuration using 4 disks (3 disks is the minimum).Ī RAID 5 array is similar to RAID 0, as data is striped across several disks. However, the usable size would only be a third of the total capacity of the disks. If you had three mirrored drives, then two disks could fail without data loss. You might think to add more disks to a RAID 1 array, but this will have the effect of dramatically increasing the cost per usable capacity. You'll need to choose your RAID hardware and software carefully to maximize read performance. However, in practice, it is usually considerably slower. For reading, in theory, the maximum speed should be the sum of the speeds of the two disks. The write performance will be the same as writing to one disk since the RAID writes the same data to both disks simultaneously. The performance, however, is nowhere near as good as RAID 0. The data is mirrored on each drive, so even if one drive fails, you still have all your data on the other drive. In contrast to RAID 0, RAID 1 is all about fault tolerance and reliability. Just make sure there is a complete copy of the data somewhere else. Preferably to magnetic tape, but you could also use on-line remote backup or a second RAID array. Please note that whatever RAID configuration you choose, you still need to backup the data. These are known as " RAID levels", and we are going to explore what they are and their characteristics in the following sections. Now there are many ways to arrange and configure these inexpensive hard disks, depending on whether you want high performance (e.g., for video editing), high reliability, low cost or something in between. It allows the creation of a single logical disk (looks like one disk from the computer's point of view) made up of many cheap hard drives. RAID is an acronym that stands for Redundant Array of Inexpensive Disks, or, occasionally, Redundant Array of Independent Disks. What was the solution? Use many disks together, acting as one. Soon cheaper hard drives came along, but they were not very reliable at all, with failures being all too common. The thing is that when they failed (everything fails eventually), all of the data would be lost (unless you had a backup) and the expensive disk would need to be replaced. In the early days of computing, mainframes used large and expensive hard disks, designed to be highly reliable. All other trademarks or registered trademarks are the property of their respective owners.If this is your first time configuring a RAID array, you might be unsure as to exactly what one is. Seagate, Seagate Technology, the Spiral logo are trademarks or registered trademarks of Seagate Technology LLC or one of its affiliated companies in the United States and/or other countries.
Seagate reserves the right to change, without notice, product offerings or specifications. Actual data rates may vary depending on operating environment and other factors. Actual quantities will vary based on several factors, including file size, file format, features and application software.
Quantitative usage examples for various applications are for illustrative purposes. In addition, some of the listed capacity is used for formatting and other functions, and thus will not be available for data storage. Your computer’s operating system may use a different standard of measurement and report a lower capacity. * When referring to drive capacity, one gigabyte, or GB, equals one billion bytes and one terabyte, or TB, equals one trillion bytes.
0 kommentar(er)
