What is the battery on a RAID controller for?
As you probably know, a RAID disk controller is a system failsafe feature that allows for a disk in a disk array to fail without bringing the system down. Built into the RAID controller is a buffer. And this cache buffer has a battery to keep the data in the cache buffer safe until it gets written to the disk drives.
RAID is an acronym that stands for Redundant Array of Inexpensive Disks or Redundant Array of Independent Disks. RAID is a term used in computing. With RAID, several hard disks are made into one logical disk. To get more flexibility (Disks can be changed or added while the system keeps running)
- Originally, the term RAID was defined as redundant array of inexpensive disks, but now it usually refers to a redundant array of independent disks. RAID storage uses multiple disks in order to provide fault tolerance, to improve overall performance, and to increase storage capacity in a system.
- Disk mirroring, also known as RAID 1, is the replication of data to two or more disks. Disk mirroring is a good choice for applications that require high performance and high availability, such as transactional applications, email and operating systems.
- RAID 2 is a technique that stripes data at the bit level using a Hamming code to detect errors. Because the error correction codes in today's hard disk drives use Hamming code, RAID 2 is now considered obsolete.
RAID was originally an acronym for Redundant Array of Inexpensive Disks, but that has since morphed into the more commonly accepted Redundant Array of Independent Disks. As its name implies, RAID is a way to pair multiple drives together to improve performance, redundancy, or both.
- RAID 01, also called RAID 0+1, is a RAID level using a mirror of stripes, achieving both replication and sharing of data between disks. The usable capacity of a RAID 01 array is the same as in a RAID 1 array made of the same drives, in which one half of the drives is used to mirror the other half.
- AHCI stand for Advance Host Controller Interface. AHCI is a hardware mechanism that allows software to communicate with Serial ATA (SATA) devices (such as host bus adapters) that are designed to offer features not offered by Parallel ATA (PATA) controllers, such as hot-plugging and native command queuing (NCQ).
- An expansion slot is a socket on the motherboard that is used to insert an expansion card (or circuit board), which provides additional features to a computer such as video, sound, advanced graphics, Ethernet or memory. With a backplane system, up to 19 expansion cards can be installed.
A disk array controller is a device which manages the physical disk drives and presents them to the computer as logical units. It almost always implements hardware RAID, thus it is sometimes referred to as RAID controller. It also often provides additional disk cache.
- The minimum number of disks in a RAID 5 set is three (two for data and one for parity). The maximum number of drives in a RAID 5 set is in theory unlimited, although your storage array is likely to have built-in limits. However, RAID 5 only protects against a single drive failure.
- RAID 0 vs. RAID 1. RAID (redundant array of independent disks) is a storage technology that combines multiple disk drive components into a single logical unit so it behaves as one drive when connected to any other hardware. RAID 1 offers redundancy through mirroring, i.e., data is written identically to two drives.
- A classic RAID 5 only ensures that each disks data and parity are on different disks. Thus also with 6 disks a RAID 5 can only recover from a single disk failure at a time. For simultaneous failures of two disks you would need a higher configuration with two parities like RAID 6 to ensure no data loss.
Updated: 25th November 2019