Hitachi STORAGE 9900 - Manual (Page 78)

Metadata
Data about data as used by the CM-HSM and the Control Memory Subsystem of the
Lightning 9900 V Series.
Mirrored Pair
Two disk units or logical units that contain the same data. The operating system
software refers to them as one entity and “reads from either” and “writes to both” when
RAID-1 is enabled.
Mirroring
A term to describe the process of writing data to two disk volumes, usually to ensure
high availability in case one of the disks fails. Mirroring can be hardware or software
based.
MPLF
The Lightning 9900 ™ V Series supports the Multiple Path Locking Facility (MPLF) for
the IBM ® highest performance transaction processing operating system – TPF. In either
native TPF mode or under VM, MPLF provides extremely high performance record-
level locking so that multiple hosts can read and write to the same file without
interfering with each other. See also TPF.
MTBF
Mean Time Between Failure. A commonly used measure of system reliability, usually
expressed in hours. Modern disk drives typically have an MTTR of 1 million hours or
more.
MTTR
Mean Time To Repair. Includes the time taken to diagnose the failure, replace or repair
faulty component(s), and restart the system so it is available to users. See MTBF.
NanoCopy ™
NanoCopy is a feature of the Hitachi Freedom Storage ™ Lightning 9900 ™ V Series
product line that enables time-consistent snapshots to be taken without stopping
applications to flush in-flight data to disk. Since there is no system impact in taking a
NanoCopy snapshot, snapshots can be made more frequently for faster recovery in the
event of a failure. See also Hitachi TrueCopy
™ , Hitachi ShadowImage ™ .
NAS
Network Attached Storage or NAS ser vers are a special class of server that allows files
to be stored over networks using the UNIX
® of Microsoft ® Windows ® remote file
system standards.
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