[Simh] Excess IOs running SIMH on Windows/XP

[Brian Knittel]

If someone wants to do an experiment, here is the information
I have about the way to change the list of files covered
by System Restore on Windows XP and Vista.

On XP, there is "super-hidden" file named 
\windows\system32\restore\filelist.xml that specifies 
the file types and directories covered by System Restore.
This file has the System, Hidden and Readonly attributes
set. Log on as an Administrator and in a Command Prompt
window type:

   cd \windows\system32\restore
   attrib -s -h -r filelist.xml
   notepad filelist.xml

This file has elements named <FILES> and <DIRECTORIES>
and <EXTENSIONS>, with <Include> and <Exclude> elements within 
each. Not too hard to decypher. I don't know what extension 
you're using for your VAX disk images, but I see that DSK 
is listed in the <EXTENSIONS><Include> section.

So -- if someone wants to experiment with this on XP,
how about excluding the directory that contains
your VAX disk images by adding a new <REC> entry
inside <DIRECTORIES><Include>, in the form 
<REC>c:\path\to\vax\files</REC>. Also, be sure that
System Protect is ON on the drive that holds
your VAX disk images.

Restart XP, log on as an Administrator, and request that 
it take a System Restore point by following these steps:

1. Click Start, All Programs, Accessories, System Tools,
   System Restore.

2. Select Create a Restore Point and click Next

3. Enter a description e.g. "Test after excluding VAX directory"

4. Click Create

Wait until disk activity ceases, then try running the
VAX simulator. Does the disk activity problem occur?

On Vista, System Restore, and on Business/Enterprise/Ultimate,
the Complate PC Backup and "Previous Files" features, are handled 
by the Volume Shadow Copy service, so entire files are not
copied all at once as on XP. Original versions of changed blocks 
are archived one at a time. 

Tecnnically, you can't guarantee exclusion from coverage
by System Restore on Vista, since the backup occurs at the
block level, below the file system. But you can "advise" it to
try to avoid specified files. It's done in the registry under
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\BackupRestore\FilesNotToSnapshot

There is probably no no compelling reason to try to exclude the 
VAX disk images from coverage under Vista. Only changed blocks are 
copied so it won't consume much time or space. I suppose if
you ever restore the disks from virtual tape, you'd be doing
double the work there. 

I'd be interested in knowing if this does turn out to
be the answer to the VAX disk activity issue.

Regards
Brian



Brian

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