Areca ARC-1110 manual Hot Spare, Hardware RAID versus Software RAID, Hot Swap, Parity, PCI Express

GLOSSARY

Hot Spare

An extra physical disk drive in a RAID configuration that a controller can use to automatically rebuild a system drive when another drive fails. The hot spare drive must have at least as mush capacity as the largest disk drive in the array or the rebuild will not start.

Hardware RAID versus Software RAID

Beyond the different types of RAID, there are two implementation forms: hardware-based and software-based. Hardware-based RAID is obviously implemented at a physical level, whereas software-based RAID is done using the operating system. It is always optimal to have RAID done at a physical (hardware) level.

Hot Swap

To pull out a component from a system and plug in a new one while the power is still on and the unit is still operating.

NVRAM

(Non-Volatile Random Access Memory) A memory unit is equipped with a battery so that the data remain even after the main power had been switched off. Actually an EEPROM used to store configuration informa- tion.

Parity

A technique used to protect a system from data loss due to faults. When parity is implemented (RAID3 and RAID5), data written is logi- cally XOR’d together to calculate parity, which is stored on the drives along with the data. In a system with three drives, the data is written to two drives and the calculated parity is stored on a third drive. If one drive fails, data on the failed drive is reconstructed from other data and parity.

PCI Express

An advanced version of the PCI bus introduced in 2002. Rather than the shared, parallel bus structure of PCI, PCI Express provides a high-

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