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January 2005

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Document:	AN-038
Order Number:	XX-EA3CE-FB
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Pages:	2
Original Filename:	AN-038.pdf

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CHARON-VAX application note
AN-038 Replacing legacy removable storage with CHARON-VAX
Author:

Robert Boers

Applies to:

CHARON-VAX products for the Windows platform

Date: 3 January 2005

Modern removable PC storage components - for instance USB 'dongles' - were created long after VAX
system development was terminated. For VAX systems, such removable storage needs were often
met by - much more expensive and much slower - magnetic or optical removable drives, and these
configurations are still in use on VAX systems today.
When replacing VAX systems with CHARON-VAX, the SCSI versions of such legacy storage devices
can be connected to the emulator, but this implies retaining the old drive hardware with its
maintenance implications. An elegant alternative in CHARON-VAX is to replace the removable storage
media with compact modern devices, for instance USB or SD card storage devices, which are
available with capacities >1 GB. They offer additional advantages: low-cost per MB, rugged
construction and high operational speed.
Since CHARON-VAX can store VAX disk as disk images, the removable media could be represented
as a disk image (essentially a Windows file) on a USB solid state disk. However, this relies on the
Windows file system, and requires that the specific Windows file name is included in the CHARONVAX configuration. For a general exchange method this is inconvenient, as a different file name would
require a CHARON-VAX reconfiguration and restart.

Solution
An exact operational equivalent for the legacy VAX removable drives can be created by using PC
removable storage directly as a VAX/VMS formatted medium. The MSCP controllers in CHARON-VAX
(V3 and later) are designed to completely bypass Windows and directly access a PC removable
storage device via its 'PhysicalDriveN' identification. As with legacy removable storage, device
connection and removal are detected, the VMS INIT, MOUNT and DISMOUNT operations can be
performed and the device information (drive size, label, etc) is available to VAX/VMS.

Implementation
Obtain the removable storage device ID by inserting the storage device and use the Windows disk
manager (Right-click on "my Computer", manage, disk-management. In the list of devices you will find
e.g. Disk 1, Removable). Configure in your CHARON-VAX system an MSCP drive as PhysicalDriveN,
where N is the number of the disk drive as displayed in the Windows disk manager.
CHARON-VAX will configure a drive, even if the storage device is not connected at boot time. Once
CHARON-VAX is loaded and VAX/VMS started you can insert and mount the USB disk (the VAX/VMS
INIT command will format a new device as usual). After any R/W operations you can dismount and
physically unplug it. Subsequently you can insert any other USB disk (even of very different size) and
mount it as usual.

©2005 Software Resources International. This document is provided for information only and is not a legally binding offer.
Software Resources International reserves the right to change the product specifications without prior notice or retire the
product. The CHARON name and its logo are a registered trademark of Software Resources International.

CHARON-VAX application note AN-038
If you issue a VMS mount command for the drive without the drive being connected, VMS will
generate as usual an operator request to mount the drive. Inserting the USB device will be reported to
VAX/VMS and the drive is mounted.
A certain protection is provided in case the device is unplugged without dismounting in VMS. The
device will remain visible, but R/W operations generate device errors (such errors are noted in the
CHARON error log). However, it is possible to recover gracefully by simply issuing a VMS dismount
command, even after the device is physically removed.
Note that the USB storage device used this way has an ODS-2 format and cannot be read by the
Windows operating system.
The following is an extract from a CHARON-VAX/6610 configuration file, showing the definition of a
removable physical drive (A USB Jetflash disk in this case) as DUA4: in VAX/VMS:
# Define the VAX 6610 disk controller
Load KDM70 PUA xmi_node_id=10
Set PUA container[0]="C:\Program Files\CHARON-VAX\webdemo 6610\vms73.vdisk"
Set PUA container[2]="C:\Program Files\CHARON-VAX\webdemo 6610\users.vdisk"
Set PUA container[3]="C:\Program Files\CHARON-VAX\webdemo 6610\archive.vdisk"
# The next drive is a USB storage device
Set PUA container[4]="\\.\PhysicalDrive1"

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