Re: shared disk (DOS)

[Jakob Bohm]

On 2021-04-12 21:18, Tomas By wrote:

On Mon, 12 Apr 2021 11:16:21 +0200,Peter Maydell wrote:

No, that doesn't work. [...]

On Mon, 12 Apr 2021 12:17:08 +0200, Peter Maydell wrote:

In theory if the different guests all access entirely disjoint
sections of the file this could be made to work. [...]

They can access the exact same data also, it would just mean some
delay for one or more of them, and maybe some arbitrary decision about
the sequence.

(But if they use SHARE.EXE on the DOS side, as I understand it to
work, then there will not be concurrent access to the same DOS
files. And then it's a question of the mapping from those to image
file locations.)

You still misunderstand SHARE.EXE (a DOS only thing).  SHARE.exe makes
DOS handle file locking calls (which cc:mail may happen to use for
something).  It does nothing for sharing disks.

With network file systems such as SMB and/or NFS, SHARE.exe may also
provide some of the glue needed for file locking calls from programs
(like cc:mail) to reach the file server (which will have code to
handle locking from multiple DOS machines accessing the same file).

In general, you should treat qemu virtual machines almost like real
machines.  Wiring multiple machines to access a single physical disk
will involve use of SCSI cables coming out the back of the computer and
connected to a single physical disk.  This has always been an exotic
thing to do, and it was never supported by DOS.

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Jakob Bohm, CIO, partner, WiseMo A/S. https://www.wisemo.com
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