Maximum number of UFS snapshots

Andrea Venturoli ml at
Wed Nov 8 13:42:49 UTC 2017


I read an UFS filesystem can have up to 20 snapshot.

Looks like this is fixed in the kernel sources(*) and cannot be increased.

(*) sys/ufs/ffs/fs.h reads:

> /*
>  * The maximum number of snapshot nodes that can be associated
>  * with each filesystem. This limit affects only the number of
>  * snapshot files that can be recorded within the superblock so
>  * that they can be found when the filesystem is mounted. However,
>  * maintaining too many will slow the filesystem performance, so
>  * having this limit is a good idea.
>  */
> #define FSMAXSNAP 20

I wonder if this is something that can be changed.
Leaving performance considerations aside, what would this imply?

Inability to read previously formatted UFS filesystems? Impossibility to 
share UFS filesystems with other machines?
Superblock growing beyond its maximum size?
Anything else?

  bye & Thanks

P.S. This is mainly out of curiosity. Although such a FS would fit my 
needs, I'm not reckless enough to try this in production :)

More information about the freebsd-questions mailing list