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Фрагмент инструкции
HP RAID Software for OpenVMS,
SPD 46.49.12
Version 3.0A
• more I/O requests serviced per unit time due to prob-
virtual disk units created by RAID Software can be initial-
abilistic load balancing, or
ized as FILES-11 ODS2 or ODS5 or any other volume
structure.
• higher data transfer rate due to concurrent transfer of
data to or from more than one disk to satisfy a single
Each virtual disk created by RAID Software is a single
request.
management entity. The storage administrator should
use appropriate storage management procedures (such
as backups) with virtual disks, which can be consider-
Features Applicable to RAID Level 5 Arrays
ably larger than typical physical disks. Once a collection
The usable capacity of RAID Level 5 array is approxi-
of physical disks is bound into an array, it is not possi-
mately given by:
ble to retrieve data directly from the array’s individual
member disks.
Usable Capacity = (N-1) * 0.99 * CS
Where N is the number of physical disks in the array.
Performance of RAID Software for OpenVMS
CS is the capacity of the smallest disk in the array.
The primary purpose of RAID for OpenVMS RAID Level
0 arrays is to enhance application performance by im-
RAID Software protects against loss of data and loss of
proving I/O request processing and/or data transfer rate.
data accessibility due to the failure of any single disk in
RAID Level 0 technology normally implies a reduction in
a RAID Level 5 array. If a disk in a RAID Level 5 ar-
data reliability. The storage administrator can improve
ray fails, RAID Software provides continued service to
data reliability by increasing backup frequency or using
applications by regenerating the failed disk’s data using
RAID Software in conjunction with Volume Shadowing
information from the array’s remaining disks. (For full
for OpenVMS.
protection against loss of data availability due to single
hardware failures, RAID Software can be used in con-
The primary purpose of RAID Software Level 5 arrays is
junction with redundant hardware and supporting soft-
to improve data reliability. It may provide the secondary
ware throughout the system.)
benefit of improved performance (due to load balanc-
ing) for applications whose I/O workload consists largely
While a RAID Level 5 array is reduced by a failed disk,
of reading data. For applications with mostly write I/O
data can be read and written, but no redundancy is pro-
workloads, RAID Software Level 5 arrays may provide
vided. A second disk failure while an array is reduced
lower I/O performance than conventional disks because
prevents application access to the data stored on the
it must update redundant information each time an ap-
array, and may result in data loss.
plication writes data.
RAID Software reconstructs the contents of a failed disk
The storage administrator should understand applica-
if a replacement disk is assigned to it. Reconstruction
tion I/O characteristics and weigh the relative priorities
does not interrupt application access to data on the ar-
of performance, equipment cost, and data reliability to
ray, although performance may be affected. Replace-
determine whether RAID Software is appropriate for use
ment disks may either be assigned to RAID Software
with a given application.
by the storage administrator (using a DCL command) or
they may be placed in a spareset associated with one
or more RAID Level 5 arrays. If a disk in a RAID Level
HARDWARE REQUIREMENTS
5 array with an associated spareset fails, RAID Soft-
RAID Software is supported when used with the VAX, Al-
ware automatically acquires a replacement disk from the
pha, and I64 processors and supported OpenVMS clus-
spareset and performs reconstruction without storage
ter configurations. See the Software Requirements sec-
administrator intervention.
tion for the qualified OpenVMS versions. RAID Software
may be installed in an OpenVMS cluster configuration
of any size supported by OpenVMS Software, but the
RAID Software has been qualified to run on a maximum
of 20 nodes within a single OpenVMS cluster configu-
Using RAID Software for OpenVMS
ration.
To use RAID Software for OpenVMS, the storage ad-
RAID Software requires a minimum of 1 (for RAID Level
ministrator first creates an array using DCL functions
0) or 3 (for RAID Level 5) and a maximum of 32 physical
supplied with the software. This destroys any data previ-
disks for each array. Up to 50 arrays may be created
ously stored on the disks and creates the data structures
in a single OpenVMS cluster. Disks, storage elements,
required to manage the array. The member disks of a
(and the subsystem configurations that contain them)
RAID Software array are ODS-2 structured volumes, so
are supported by the OpenVMS Operating System Ver-
OpenVMS mechanisms protect against inadvertent mis-
sions (see Software Requirements) through the follow-
use of members for the life of the array. However, the
ing device drivers shown in Table 1.
2
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