Lenovo ThinkServer RD240 MegaRAID SAS Software User Guide - Page 354

IO policy, learning cycle, load-balancing, media error, count, migration, mirroring, multipathing

Page 354 highlights

IO policy learning cycle load-balancing media error count migration mirroring multipathing name non-redundant configuration 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.) A battery calibration operation performed by a RAID controller periodically to determine the condition of the battery. 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. A drive property indicating the number of errors that have been detected on the drive media. 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. 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. 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. A virtual drive property indicating the user-assigned name of the virtual drive. 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. B-6 Glossary

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B-6
Glossary
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.
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.