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i386/92723: fdisk should be able to output current slice table in configuration file format



>Number:         92723
>Category:       i386
>Synopsis:       fdisk should be able to output current slice table in configuration file format
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    freebsd-i386
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          change-request
>Submitter-Id:   current-users
>Arrival-Date:   Thu Feb 02 08:30:05 GMT 2006
>Closed-Date:
>Last-Modified:
>Originator:     Jukka Ukkonen
>Release:        6.0-STABLE
>Organization:
private person
>Environment:
FreeBSD metabo 6.0-STABLE FreeBSD 6.0-STABLE #4: Mon Jan 30 22:45:06 EET 2006     root@metabo:/usr/obj/usr/src/sys/Metabo  i386
>Description:
              Currently fdisk writes only verbose output.

1) Often it would be nice to be able to clone the fdisk slice setup to
another disk of the same model (say you are preparing mirrored volumes).

2) Often it would be nice to be able to store the exact fdisk slice setup
as a backup in case you need to replace and rebuild a disk.
I tend to dump the contents of file systems and the current disklabel
(bsdlabel) when doing backups. Having also the slice table stored safely
in a reusable format would help complete disk rebuilding a lot.

In both of the previous situations it would be preferable to have fdisk to
output the read slice table in the configuration table format to be able
to further feed it to another fdisk instance as input.

At the moment this is not possible or at least not a documented feature.
A good configuration program should always be able to write out the same
format it requires on input.

>How-To-Repeat:
              OK - just try to recreate from scratch some disk you already have
such that there is one slice for actual file system and another for swap.
Obviously you might wish to mirror the file system slice, but since the swap is
ephemeral data and used in interleaved manner in any case, you do not wish to
mirror the swap area. You simply specify two independent swap areas.

So, assume you build a mirror from two disks with suitable slices for the
above schenario, but you use disks which are not equal in size. Now just assume
you will need to rebuild the larger disk, because the old one has a hardware
failure.
Currently you cannot copy the slice tables, and even if you could, you would
prefer to rebuild the slice table on the replaced disk from a backup copy,
because there larger disk might have had extra space sliced for other purposes.

>Fix:
              Extend fdisk with a new command line option and a whole new feature.

>Release-Note:
>Audit-Trail:
>Unformatted: