Avago Technologies MegaRAID Fast Path Software - Manual (Page 494)

Page 494 LSI Corporation Confidential | July 2011
MegaRAID SAS Software User Guide Appendix C: Glossary
initialization The process of writing zeros to the data fields of a virtual drive and, in fault-tolerant
RAID levels, generating the corresponding parity to put the virtual drive in a Ready
state. Initialization erases all previous data on the drives. Drive groups will work without
initializing, but they can fail a consistency check because the parity fields have not
been generated.
IO policy A virtual drive property indicating whether Cached I/O or Direct I/O is being used. In
Cached I/O mode, all reads are buffered in cache memory. In Direct I/O mode, reads are
not buffered in cache memory. Data is transferred to cache and the host concurrently. If
the same data block is read again, it comes from cache memory. (The IO Policy applies
to reads on a specific virtual drive. It does not affect the read ahead cache.)
learning cycle A battery calibration operation performed by a RAID controller periodically to
determine the condition of the battery.
load-balancing A method of spreading work between two or more computers, network links, CPUs,
drives, or other resources. Load balancing is used to maximize resource use,
throughput, or response time.
LKM Local Key Management
media error count A drive property indicating the number of errors that have been detected on the drive
media.
migration The process of moving virtual drives and hot spare drives from one controller to
another by disconnecting the drives from one controller and attaching them to
another one. The firmware on the new controller will detect and retain the virtual drive
information on the drives.
mirroring The process of providing complete data redundancy with two drives by maintaining an
exact copy of one drive’s data on the second drive. If one drive fails, the contents of the
other drive can be used to maintain the integrity of the system and to rebuild the failed
drive.
multipathing The firmware provides support for detecting and using multiple paths from the RAID
controllers to the SAS devices that are in enclosures. Devices connected to enclosures
have multiple paths to them. With redundant paths to the same port of a device, if one
path fails, another path can be used to communicate between the controller and the
device. Using multiple paths with load balancing, instead of a single path, can increase
reliability through redundancy.
name A virtual drive property indicating the user-assigned name of the virtual drive.
non-redundant configuration A RAID 0 virtual drive with data striped across two or more drives but without drive
mirroring or parity. This provides for high data throughput but offers no protection in
case of a drive failure.
NVRAM Acronym for non-volatile random access memory. A storage system that does not lose
the data stored on it when power is removed. NVRAM is used to store firmware and
configuration data on the RAID controller.
NVRAM present A controller property indicating whether an NVRAM is present on the controller.
NVRAM size A controller property indicating the capacity of the controller’s NVRAM.
offline A drive is offline when it is part of a virtual drive but its data is not accessible to the
virtual drive.