[Info-vax] Hard links on VMS ODS5 disks

[Stephen Hoffman]

On 2023-07-12 13:34:35 +0000, Chris Townley said:

> I am just about to install V9.2-1 and intrigued about hard links.
> 
> When I installed E9.2-1 it asked me if I wanted to enable hard links, 
> with a warning to read the docs, but I wasn't much wiser afterwards.
> 
> I get he impression that it is much cleaner with them enables, but what 
> are the downside risks?
> 
> I have used soft links on *nix for many years, but only for linking to 
> a directory, which you cannot do with hard links
> 
> Any thoughts?

Enable hardlinks, run ANALYZE /DISK /REPAIR, and continue with whatever 
you were doing.

That prompt is... ill-considered. That change should have been packaged 
and presented as a bug fix.

That change fixes a longstanding bug in the existing file system design.





Background, from most of a decade ago: "Maybe that gets better 
documented? The official documentation in the HPE 
V8.4-to-V8.2-inclusive System Manager's Manual /10.12 Understanding 
Hard Links/ appears correct but also a little conflated, and that  
material is old enough that it doesn't even mention softlinks."

That cited doc is now here: 
https://docs.vmssoftware.com/docs/vsi-openvms-system-manager-s-manual-volume-1-essentials.pdf 
page 402.

Quoth the docs: "If you have hard links enabled, a file is actually 
deleted when there are no more links to file. If you do not have hard 
links enabled, and you have not created an alias for a file, 
essentially only one link to that file exists: the primary link. If you 
create an alias for that file, and you delete the alias, the file still 
exists because the primary link to that file has not been deleted. The 
alias is just another name in a directory for this link. Deleting the 
primary link deletes the file, leaving the alias entries."
That section of the doc could be worded more clearly, and it is also 
stale as there are four sorts of links with current OpenVMS: primary 
links, aliases, hardlinks, and softlinks.

Yes, apps that rummage the file system directly might need to know. I'd 
expect a number of apps that do try to look at links probably get it 
wrong, too.





Old grumping, from most of a decade ago: "Usual solution for 
compatibility? Add knobs and APIs and run-time checks, and throw it all 
over the wall and let somebody else figure it out when — when, not if — 
it breaks.  Design abdication."


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