It's certainly do-able; we had a system like this at Interval. Basically write an image to a suitably chosen name, check if it was ok (which could involve a lot of work if you want to be paranoid) and if so rename (and check the rename worked!) and quit.
Craig might possibly have the code around? I certainly don't.

> On 2020-01-29, at 12:10 PM, Tony Garnock-Jones <tonyg at leastfixedpoint.com> wrote:
> 
> That sounds like a great idea.
> 
> On configurations where overwrite-by-rename is a problem, perhaps an
> alternate of "copy the existing image to a *.bak file" would work?
> 
> Perhaps the image save primitive could respond to a VM command-line
> switch (or in-image VM parameter?) selecting among three behaviours:
> 
> 1. The current overwrite-in-place, risk-of-corruption behaviour
> 2. Overwrite-by-rename if possible
> 3. Make backup copy before overwrite-in-place
> 
> Regards,
>  Tony
> 
> 
> On 1/29/20 6:00 PM, Thiede, Christoph wrote:
>> Hi all,
>> 
>> 
>> some months ago, I corrupted my image by accidentally shutting down the
>> host system while saving the image file (many of my images are > 500 MB,
>> so this can take a few seconds even on an SSD). The same can happen due
>> to various other IO/connection issues, so here's an idea:
>> Couldn't we always use overwrite-by-rename when saving the image file?
>> I. e., first the image into a new temporary file and, after saving
>> has completed, replace the original file with that temp file (via mv)?
>> This would ensure the image file's integrity.
>> 
>> 
>> A possible disadvantage, though, would be that some filesystems, such as
>> NTFS, associate meta-information with the file identity, which changes
>> when using the overwrite-by-rename approach. Also, technologies such as
>> FileSystemWatcher would be confused for the same reason. However, afaik
>> overwrite-by-rename is a quite common approach, in primary for big and
>> sensitive files.
>> 
>> 
>> However, what are your opinions about this topic? :-)
>> 
>> 
>> Best,
>> 
>> Christoph
>> 
>> 
>> 
> 
> 


tim
--
tim Rowledge; tim at rowledge.org; http://www.rowledge.org/tim
Oxymorons: Living dead