HP DECram for OpenVMS

Software
Product
Description
PRODUCT NAME: HP DECram for OpenVMS
SPD 34.26.12
DESCRIPTION
This Software Product Description describes the follow-
ing Versions of HP DECram for OpenVMS:
• HP DECram for OpenVMS Alpha and Integrity
servers Version 8.3
• HP DECram for OpenVMS Alpha Version 3.2
• HP DECram for OpenVMS Alpha and VAX Version
2.5
DECram for OpenVMS is a disk device driver that im-
proves I/O performance by allowing an OpenVMS sys-
tem manager to create pseudo disks (RAMdisks), which
reside in main memory. Frequently accessed data can
be accessed much faster from a DECram device than
from a physical disk device. These RAMdisks can be
accessed through the file system just as physical disks
are accessed, requiring no change to the application or
the system software.
Because main memory is allocated for a DECram de-
vice, extra memory is generally required. The Open-
VMS system manager can designate the amount of
memory dedicated to the DECram device(s) and the
files that will be stored on it.
Beginning with OpenVMS Version 8.2, the images for
HP DECram ship with the HP OpenVMS Alpha and
Integrity servers distribution kits. To run the DECram
software, customers must first purchase and install a
separate DECram or Enterprise Operating Environment
(EOE) license package.
Before upgrading to OpenVMS Alpha Version 8.2 or
higher, you must manually remove earlier versions of
DECram for OpenVMS. The upgrade procedure cannot
remove DECram for OpenVMS automatically. If an old
version of DECram for OpenVMS is installed, the up-
grade procedure might abort; if the upgrade does com-
plete, DECram for OpenVMS might cause errors or work
improperly.
Note: This requirement applies to OpenVMS Alpha sys-
tems only, and only to upgrades from any version of
OpenVMS prior to Version 8.2.
Beginning with DECram Alpha Version 3.2, DECram’s
capability was extended to use OpenVMS Galaxy
shared memory to create a VMS shared memory disk.
This allows users to take advantage of OpenVMS
Galaxy shared memory without modifications to any of
their applications.
With DECram Alpha Version 3.2 or higher, the limit on
DECram disk size is 4,294,967,296 blocks on OpenVMS
Alpha systems running OpenVMS Version 7.2-1H1 or
higher.
However, the largest value that OpenVMS supports is
2,147,483,647 for ODS-2 and ODS-5 volumes.
With DECram Version 2.5, the maximum disk size on
an OpenVMS Alpha system is limited to 67,108,864
blocks.The maximum disk size on an OpenVMS VAX
system is limited to 524,280 blocks. It is possible to
create logically contiguous devices greater than these
limits by creating multiple DECram devices and binding
them together.
Note: An actual DECram device is limited by the number
of available system page table entries (SPTEs) on the
system. A DECram device cannot be bigger than the
available physical memory of the host.
June 2006