Administrator Guide

Non-distributed consistency groups
Transfer data through one primary RPA that is designated by the user during group creation. The policies applied by the
consistency group can be modified at any time.
In the event of RPA failure, groups that transfer data through the failed RPA will move to other RPAs in the cluster.
O
Open LDAP
Open source implementation of the Lightweight Directory Access Protocol (LDAP).
P
parity checking
Checking for errors in binary data. Depending on whether the byte has an even or odd number of bits, an extra 0 or 1 bit, called
a parity bit, is added to each byte in a transmission. The sender and receiver agree on odd parity, even parity, or no parity. If
they agree on even parity, a parity bit is added that makes each byte even. If they agree on odd parity, a parity bit is added that
makes each byte odd. If the data is transmitted incorrectly, the change in parity will reveal the error.
partition
A subdivision of a physical or virtual disk, which is a logical entity only visible to the end user and not to any of the devices.
point-in-time (PIT)
See the description for Snapshot/PIT.
Production journal volumes
Volumes that hold system delta marking information.
Production volumes
Volumes that are written to by the host applications. Writes to production volumes are split such that they are sent to both the
normally designated volumes and RPAs simultaneously.
Each production volume must be exactly the same size as the replica volume to which it replicates.
R
RAID
The use of two or more storage volumes to provide better performance, error recovery, and fault tolerance.
RAID 0
A performance orientated striped or dispersed data mapping technique. Uniformly sized blocks of storage are assigned in regular
sequence to all of the arrays disks. Provides high I/O performance at low inherent cost. No additional disks are required. The
advantages of RAID 0 are a very simple design and an ease of implementation.
RAID 1
Also called mirroring, this has been used longer than any other form of RAID. It remains popular because of simplicity and a high
level of data availability. A mirrored array consists of two or more disks. Each disk in a mirrored array holds an identical image
of the user data. RAID 1 has no striping. Read performance is improved since either disk can be read at the same time. Write
performance is lower than single disk storage. Writes must be performed on all disks, or mirrors, in the RAID 1. RAID 1 provides
very good data reliability for read-intensive applications.
RAID leg
A copy of data, called a mirror, that is located at a user's current location.
rebuild
The process of reconstructing data onto a spare or replacement drive after a drive failure. Data is reconstructed from the data
on the surviving disks, assuming mirroring has been employed.
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Glossary