Subject: Re: fss questions
To: NetBSD User's Discussion List <email@example.com>
From: Juergen Hannken-Illjes <firstname.lastname@example.org>
Date: 03/16/2005 12:22:16
On Tue, Mar 15, 2005 at 10:32:25PM -0500, Louis Guillaume wrote:
> Hello All,
> I'm trying to figure out how to use fss for backup purposes.
> The way I understand it should work is like this...
> 1. make the system as quiescent as possible.
> 2. create the snapshot.
> 3. bring databases, fileservers etc. back online.
> 4. dump the snapshot to tape.
> ... this gives me a minimum of downtime for backups.
> After reading the man page for fssconfig, I'm a little confused...
A man page written by by some native english speaker would be a win :-)
> "The *fssconfig* command configures file system snapshot pseudo disk
> devices. It will associate the file system snapshot disk _device_ with
> a snapshot of _path_ allowing the latter to be accessed as though it
> were a disk. Data written through the _path_ will be saved in _backup_
> which must not reside on the snapshotted file system. 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."
> . What I get from this (and from my meagre knowledge of snapshot
> concepts) is that the blocks in "path" are pointed to by some structure
> in "device", and if one of those blocks becomes overwritten (in the
> filesystem), it is first copied to a file in "backup", and the pointer
> in the fss device is re-directed to that block in "backup".
> I feel I'm missing something, though. Where it says,
> "It will associate the file system snapshot disk `device' with a
> snapshot of `path' allowing the latter [that's `path'] to be accessed as
> though it were a disk."
After `fssconfig fss1 /share/data /tmp/backup' the snapshot of the
file system `/share/data' may be accessed through the device(s)
`/dev/rfss1' and `/dev/fss1'.
To dump: `dump 0... /dev/rfss1 ...' and to mount: `mount -r /dev/fss1 /...'.
> ... now isn't `path' a real path on the filesystem? i.e. the thing we're
> taking the snap of? Do they mean "former" rather than "latter", so the
> `device' can be accessed as a disk?
> . Now that I have this snapshot, how do I back it up. It has no
> disklabel or recognizable filesystem interface. How can I mount it to
> access the data on the snapshot?
> Any help would be greatly appreciated.
Juergen Hannken-Illjes - email@example.com - TU Braunschweig (Germany)