Support for Using the Entire Disk Space on LDEV 1

By Ushadevi H N, Commercial Systems Division

Beginning with MPE/iX 7.5 release, the MPE/iX operating system uses the full capacity of the disk configured as LDEV 1. This article explains the enhancement and briefly describes the user level changes for customers to use the system appropriately after installing MPE/iX 7.5 release.

Background

Before the 7.5 release, MPE/iX limited the access on LDEV 1 to only the first 4GB of the total disk space with the rest of the disk unavailable for use.

Primarily, this limitation existed because the initial system loader (ISL> prompt) could access only the first 4GB of the disk. System utilities such as START, DUMP, and DISCUTIL need to reside in the first 4GB of the disk. As a result, LDEV 1 disk access overall was limited to 4GB of the disk space.

With this enhancement, the operating system can utilize the entire disk space for storing other files. Because the ISL limitation is not removed, system utilities still need to be stored within the first 4GB of the disk.

Hardware and Software Requirements

This enhancement is enabled by default once the MPE 7.5 version of the operating system (Release C.75.00) is installed. This feature applies to all HP supported disks and disk arrays, regardless of the disk capacity.




	NOTE: Even though this feature is to take advantage of all disks greater than 4GB, only disks with a capacity greater than (or equal to) 5GB will have their extra capacity available for use.

Enhancement Details

For disks configured as LDEV 1, this enhancement distinguishes between files residing within 4GB and those beyond 4GB. Proper functioning of the MPE/iX operating system requires that some specific system utilities reside in the first 4GB of the disk. Therefore, user files targeted for LDEV 1 are stored in the first 4GB under only two circumstances:

If there is not enough space beyond the first 4GB to accommodate the file.
When forced by the file equate option described below.

HP highly recommends that user files be kept in the disk space beyond 4GB to preserve space for system files, now and in the future. A new designator is provided to differentiate and help users keep files within or beyond 4GB.

;DEV=**$SYSTEM_MASTER

The device designator $SYSTEM_MASTER is now used to refer to the file space within the first 4 GB of LDEV 1. Using $SYSTEM_MASTER in file commands such as BUILD and FILE, and in file intrinsics (for example, HPFOPEN) will create and refer to files within the first 4 GB.

EXAMPLE: Creating files within the first 4GB of LDEV 1

Prior to 7.5 all installation tools/applications, such as PATCH/iX, AUTOINST, HPINSTAL, AUTORESTART/iX, etc., use the following equation to create AXLDEV1 (for the purpose of reserving space):

: BUILD AXLDEV1;DISC=n,1,1;DEV=1

where n is the number determined in "Estimating Disk Space" as given in the MPE/iX System Maintenance Manual.

For 7.5 the above equation needs to be changed to:

: BUILD AXLDEV1;DISC=n,1,1;DEV=**$SYSTEM_MASTER




	WARNING! In case the requested space is not available within the 4GB, an error indicating out of space is returned (even if enough space is available beyond the first 4GB) when creating this file. OUT OF DISK SPACE (FSERR 46) To make more space within 4GB, read the section "Freeing Space within 4GB"

;DEV=1

For user files, (i.e., for non-system files) HP recommends that these files be stored in private volumes. In cases where user files are stored in LDEV 1, use ;DEV=1. By specifying ;DEV=1 during creation, the system attempts to create/store the files beyond 4GB. If the required space is not available in the area beyond 4GB, the system creates/stores the files within the first 4GB of the disk.

Freeing Disk Space within 4GB

During system update or other activities that create files on LDEV 1, you may receive OUT OF DISK SPACE (FSERR 46) errors. Even when the discfree utility shows plenty of free space, you may need to free disk space within the first 4GB of LDEV 1 to enable system files to reside there. The following method can be used to free the disk space:

To identify where files are stored on LDEV 1, use the SHOWUSAGE command in VOLUTIL:

VOLUTIL:SHOWUSAGE  1;PERM;FORMAT=DETAIL 
PERM Space on LDEV 1: processing ... SECTOR ADDRESS        SIZE (in sectors)   SPACE_USED_BY 
--------------         ------------------    -------------          48                96             MMSAVE.MPEXL.SYS 
      14128                32             MPEXLDIR.PUB.SYS 
      14160               320             ISL.MPEXL.SYS 
      14480             53904             START.MPEXL.SYS 
       68384               25120               DISCUTIL.MPEXL.SYS

The sector address of 4GB is 16777216. Any user file having an address lower than this number is a potential candidate to be moved beyond the first 4GB of disk space.

Once the files are identified, you may use the following set of commands to move the files beyond 4GB:

File t;dev=disc
Store <files>;*t
Restore *t;<files> (use the ;olddate option to retain dates before the STORE)

Generally, the files loaded at ISL > are the files that MUST reside within 4GB. The list of such files can be obtained at the ISL prompt using the LS command.

ISL> LSISL        START      DISCUTIL   SAT        DUMP       STAGEISL 
A1002AI    A1002AM    A1002AP    EDBC       EDPROC     MDIAG 
MPROC      ODE        ODEDATA    ODEDATA2   TDIAG      UNIPROC 
BCDIAG      CAEXR        XMAP        CLKUTIL     SADPATCH    AUTOBOOT

Compatibility Issues

STORE/RESTORE

If files stored from MPE/iX 7.5 are restored to a machine with a pre-7.5 OS, the following warning message may appear. This is due to the $SYSTEM_MASTER interpretation (explained above) and can be ignored. The files that show this warning are restored on LDEV 1.

COULD NOT BE RESTRICTED TO THE SYSTEM MASTER VOLUME

SYSTEM REBOOT after MPE/iX 7.5 Installation/Update

During the first boot after install/update of this version, the following message may appear on the system console (the system reports that it is mapping the entire LDEV 1 disk capacity for use):

          "relocate ssm map to(in sectors) #####" 
          "To map to the full disk size ###### in pages"

Before Backdating Your System

Important Details Please Read

Before backdating from MPE/iX 7.5 version (or later) to an earlier version of MPE/iX (like 6.0, 6.5 or 7.0), it is critical to understand that this LDEV 1 enhancement is not available in any of these pre-7.5 versions. Hence, these pre-7.5 versions of the operating system cannot differentiate whether the files are within the first 4GB of LDEV 1 or beyond it.

After backdating, pre-7.5 versions of the operating system will still be able to access the entire capacity of LDEV 1 and start filling the disk from the beginning of the available free space. As a result, system utilities, such as START and INSTALL, may be stored in the disk space beyond the first 4GB. If that occurs, the system will not BOOT. A reinstall of the system from the pre-7.5 backup would then be required.

Once the system is able to boot after the backdating, the entire disk is available for the operating system and entire disk files are available for use. However, this same risk exists every time a patch is applied to the system.

RECOMMENDATION if considering backdating from 7.5 to an older release:

HP highly recommends that the user perform an INSTALL from the pre-7.5 backup instead of backdating. Alternatively, the user could perform a full backup, INSTALL a pre-7.5 version, and then restore from the backup.