1 – DISK
Create or modify a virtual disk, memory disk, of a specified
capacity in local private memory or Galaxy shared memory.
Format
CREATE DISK disk-name
1.1 – Parameters
disk-name
The name of the memory disk that you want to create or modify.
The disk name must begin with MD followed by a controller letter
between A and Z followed by the disk number from 0 to 9999 for
served devices such as MDC256. The non-served device number
limit is 32767.
1.2 – Description
The CREATE DISK command creates or modifies a memory disk in
local private memory or Galaxy shared memory The command can be
further refined with the available qualifiers. The command
can be entered from the VMS prompt or the DECRAM> prompt.
Requires AUDIT, CMKRNL, SYSLCK, SYSPRV, and PHY_IO privileges.
1.3 – Qualifiers
1.3.1 /CAPACITY
/CAPACITY=blocks
This qualifier is required. You must specify the size of the memory
disk to create or modify in blocks (512 bytes). Capacity=0 will
return the memory to the operating system.
1.3.2 /MEMORY
/MEMORY=type
This qualifier is not required and defaults to local. LOCAL means
create the memory disk in local private memory. SHARED means create
the memory disk in Galaxy shared memory. Local memory can be accessed
on only the node or instance where it resides. Shared memory can be
accessed from any Galaxy instance that attaches to the shared memory.
Shared memory requires VMS Galaxy software to be loaded and running.
1.3.3 /PERSIST
/[no]PERSIST
This qualifier is not required and defaults to /PERSIST. It
controls whether or not the disk is restored after a reboot.
Note that /nopersist and /serve are mutually exclusive.
1.3.4 /SERVE
/[no]SERVE
This qualifier is not required and defaults to /NOSERVE. It
controls whether or not disk serving is available for the
VMSCluster. When /SERVE is selected, the disk is MSCP
served. Once a disk is selected /SERVE it cannot be selected
/NOSERVE.
Note that /nopersist and /serve are mutually exclusive. Also
note that served device numbers cannot exceed 9999.
1.3.5 /ALLOCLASS
/ALLOCLASS=number
This qualifier is not required and defaults to 99. It is only
allowed for SHARED memory type disks. Note that associating a
particular controller letter with a specific allocation class
is valid for all time! All time means as long as the shared
memory section exists or the MDRECOVER.DAT file exists. Selecting
an allocation class equal to the node's allocation class for
shared memory disks is not allowed.
1.3.6 /WRITEBUFFERED
/[no]WRITEBUFFERED
This qualifier is not required and defaults to /NOWRITEBUFFERED.
It is selected to help reduce write recovery time after a power
fail or system crash. Application recovery techniques and OpenVMS
Volume Shadowing can also be used to reduce write recovery time
after a power fail.
1.3.7 /RAD
/RAD=stripe (default)
/RAD=number
/RAD=home
/RAD=(,,,)
This qualifier is not required and defaults to striping the
memory disk across all available RADs for local and shared disks.
It is only effective when RAD SUPPORT is enabled on the system.
It is used to specify a single RAD (i.e., a number such as 2) for
both local and shared memory, or a comma separated list of RADs
for shared memory only. It can also be used to select the home RAD
or to change from a single RAD to striping.
1.4 – Examples
1. $ decram create disk mdf1111 /capacity=16777216 /memory=local -
/serve /nopersist /rad=2
This example creates an 8 gigabyte memory disk mdf1111 in local
memory with an allocation class equivalent to the node allocation
class. It is issued from the VMS prompt. It will not persist at
the next reboot but disk serving to the VMScluster is enabled.
If the system has RAD SUPPORT enabled then RAD 2 will be used
to create the disk otherwise OpenVMS will pick the RAD(s).
2. DECRAM> create disk mda0 /cap=1000034 /mem=shared /rad=(0,1)
This example creates memory disk $99$mda0 in shared memory RAD 0
and RAD 1 with a size of 1,000,034 blocks and allocation class
99. It is issued from the DECRAM> prompt. It will persist at the
next reboot but disk serving to the VMScluster is not enabled.
3. DECRAM> create disk mdb0 /cap=10000 /mem=shared /alloc=13
DECRAM> create disk mdb1 /cap=10000 /mem=shared /alloc=13
$ init $13$mdb0 $13$mdb0
$ mount dsa0: /shadow=($13$mdb0:,$13$mdb1:) $13$mdb0
This example creates two 10000 block shared memory disks with
allocation class 13. One of them is initialized and a VMS
Volume shadow set is made from the two memory disks. The memory
disks are not served to the cluster.
4. VMS Galaxy Instance 0
$ decram create disk mdb0 /capacity=10000 /memory=shared
$ init mdb0 mdb0
$ mount /cluster mdb0 mdb0
$ show device mdb0
Device Device Error Volume Free Trans Mnt
Name Status Count Label Blocks Count Cnt
$99$MDB0: (BANG) Mounted 0 MDB0 9967 1 2
VMS Galaxy Instance 1
$ decram create disk mdb0 /capacity=10000 /memory=shared
$ show device mdb0
Device Device Error Volume Free Trans Mnt
Name Status Count Label Blocks Count Cnt
$99$MDB0: (BIG1) Mounted 0 MDB0 9967 1 2
This example assumes a two instance VMS Galaxy with DECRAM V3
installed on both instances. It creates two 10000 block shared
memory disks with allocation class 99. One of them is created on
instance 0 and the other on instance 1. The shared disk is
initialized and mounted cluster-wide from instance 0. Note that
if a shared disk has been created on each instance the
"$ decram create disk" command is only necessary on one instance.