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Comment: PCI I/O Bypass controller chapter is added

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geometry

Parameter

geometry [N] 

N is 0..32766 (no more than 64 units)

TypeText String
Value

This formatted string value specifies the explicit geometry of the disk storage element. This parameter is not applicable to tape storage elements.

The string format is ”*/*/*/<B>" or ”*,*,*<B>" where B is the total size of the disk (in blocks) reported to the guest OS. If omitted it is calculated automatically.

If this parameter is not set, CHARON VM will configure the geometry based on the most probable disk type.

Initially not set.

Info

It is possiblle to specify each parameter independently of another one. The following syntax is used for that:

set DIA geometry[300]="*,*,*,16777210"

use_io_file_buffering

Parameter

use_io_file_buffering[N]

N is 0..32766 (no more than 64 units)

TypeText String
Value

Instructs CHARON VM to enable host operating system I/O cache on reading/writing operations.

The following values are possible:

  • "true" or "write-back" - the "write back" caching mode is used

  • "write-through" - the "write through" caching mode is used

  • "false" - caching is switched off

(info) Note that this caching has a significant effect only in case of mapping to disk and tape containers, not physical drives.

When enabled, host operating system I/O cache may significantly improve I/O performance of the virtual system. At the same time maintaining I/O cache requires additional host resources (CPU and memory) which may negatively affect overall performance of the virtual system.

Initially is set to "false".

Example:

set PKA DIA use_io_file_buffering[603]=true


When a tape or disk image connected to an emulated KZPBA controller is an I/O Bypass controller is dismounted by OpenVMS, it is disconnected from CHARON VM and can be manipulated. It can be replaced with a different disk image if it keeps the same name. This capability may be useful when designing back-up and restore procedures. When copying CHARON-AXP disk images while CHARON VM is running, please take care to minimize the risk of overloading a heavily loaded CHARON host system. For example, using a sequential series of simple ftp binary copies is less resource intensive and thus less disruptive than multiple, simultaneous copies.

Empty disk images are created with the "MkDisk" utility. Tape images ("*.vtape" ) will be created automatically if they don't exist (no utility needed).

CHARON-AXP is able to boot from disk images of any OpenVMS/Alpha and Tru64 version.

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The virtual KZPBA storage controller examines the file extension (vdisk or vtape) to distinguish between a disk image and a tape image.

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