Subject: Re: dump -x
To: Louis Guillaume <>
From: Stephen Borrill <>
List: netbsd-users
Date: 05/09/2007 09:06:35
On Wed, 9 May 2007, Louis Guillaume wrote:
> I've been using fssconfig to create snapshots of my filesystems and then
> dumping them to tape.
> But I just noticed the -x and -X options on the dump(8) man page...
> -x snap-backup
>         Use a snapshot with snap-backup as backup for this dump.  See
>         fss(4) for more details.  Snapshot support is experimental.  Be
>         sure you have a backup before you use it.
> -X      Similar to -x but uses a file system internal snapshot on the
>         file system to be dumped.
> 3 things:
> (1) What has to be done to make fss no longer experimental? I have and
> only good results (except when creating snapshots of LFS filesystems).

What NetBSD version? I found it hung the machine about once a week when 
ran nightly and so had to stop using it in production.

> (2) What's a `file system internal snapshot'?
> (3) Is there any more information on the -x option? I'd like to know the
> parameters it uses for fssconfig.

Isn't this the difference between placing the backup file on the 
snapshotted file system or not? From fssconfig(8):

"If backup resides on the snapshotted file system a persistent snapshot
will be created.  This snapshot is active until backup is unlinked. 
This snapshot mode is only supported for ffs files systems.

Otherwise data written through the path will be saved in backup.  If
backup is a regular file, it will be created with length size. 
Default size is the size of path.  Data is saved to backup in units of 
cluster bytes."