virtualbox.org

hello
I wonder whether having a couple of snapshots will noticeably affect guest disk performance or not.
Do you know any documents about it?
Did anybody measure such influence?

regards for all

I think that you will only notice it if you run a program that uses a lot of I/O. The difference however will not be that much. You will notice more between an HDD and SSD than when you have snapshots. It is true that files are eventually spread across several snapshots and all those files have to be searched for it, but as you modify those files, they will end up in newer snapshots anyway, so that seek time will be reduced too.

So, only if you have a ridiculous amount of snapshots with files in them that are accessed, but not modified (though, some OSes mark a file that's accessed as modified as well because of the access timestamp), you will notice it. But it will be mere milliseconds of waiting for a file to be accessed, something you would not notice in the end.

Sasquatch wrote:It is true that files are eventually spread across several snapshots and all those files have to be searched for it

Actually that isn't true. VBox will have the chain of block tables resident in memory - effectively a resident lookup table - so no searching on disk is ever required. When the disk access occurs (the only thing that takes a significant time), it will always be to the correct snapshot file. If course there is an additional scope for host fragmentation that would only be noticed in extreme cases.

Snapshots take up too much space on disk, are too awkward to manage, and too risky to use (IMHO)... but performance should not really be a concern.