Filter
Top Products
GLOSSARY
176
Hot Spare
An extra physical disk drive in a RAID conguration 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 conguration 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-