How to add unused space to an existing install

dteske at dteske at
Wed Feb 6 23:21:35 UTC 2013

> -----Original Message-----
> From: owner-freebsd-questions at [mailto:owner-freebsd-
> questions at] On Behalf Of Paul Schmehl
> Sent: Wednesday, February 06, 2013 9:59 AM
> To: FreeBSD Questions List
> Subject: How to add unused space to an existing install
> I have a FreeBSD 8.3 RELEASE box that we recently discovered only has part
> of the "disk" being used.  This box has four 1TB drives in RAID 5, and df
> only shows 500MB of disk available.
> fdisk shows this:
> # fdisk -p
> # /dev/mfid0
> g c364602 h255 s63
> p 1 0xa5 63 1562363771
> a 1
> When I run the fdisk editor in sysinstall I see this:
> Disk name:      mfid0                                  FDISK Partition
> Editor
> DISK Geometry:  364602 cyls/255 heads/63 sectors = 5857331130 sectors
> (2860024MB)
> Offset       Size(ST)        End     Name  PType       Desc  Subtype
> Flags
>          0         63         62        -     12     unused        0
>         63 1562363771 1562363833  mfid0s1      8    freebsd      165
> 1562363834 4294981702 5857345535        -     12     unused        0
> I want to capture all that unused space and add it to the server.
> fstab has this:
> # cat /etc/fstab
> # Device		Mountpoint	FStype	Options		Dump
> 	Pass#
> /dev/mfid0s1b		none		swap	sw		0	0
> /dev/mfid0s1a		/		ufs	rw		1	1
> /dev/mfid0s1e		/home		ufs	rw		2	2
> /dev/mfid0s1d		/tmp		ufs	rw		2	2
> /dev/mfid0s1f		/usr		ufs	rw		2	2
> /dev/mfid0s1g		/var		ufs	rw		2	2
> /dev/acd0		/cdrom		cd9660	ro,noauto	0	0
> When I try to create a new slice using fdisk, it doesn't seem to work.

Did you try something like:

echo "p 2 165 * *" | sudo fdisk -f- /dev/mfid0


Afterward "fdisk -p" should show something like...

# /dev/mfid0
g c364602 h255 s63
p 1 0xa5 63 1562363771
p 2 0xa5 <num> <num>
a 1

And then you'll have /dev/mfid0s2 which you can do-with what you like (directly
newfs the slice or create BSD partitions underneath that to further sub-divide
into as many as 8 smaller units, /dev/mfid0s2[a-h]).

> If I move to the label editor, I get this:
>  FreeBSD Disklabel Editor
> Disk: mfid0     Partition name: mfid0s1 Free: 0 blocks (0MB)
> Part      Mount          Size Newfs   Part      Mount          Size Newfs
> ----      -----          ---- -----   ----      -----          ---- -----
> mfid0s1a  <none>       2000MB *
> mfid0s1d  <none>      65536MB *
> mfid0s1e  <none>       4096MB *
> mfid0s1b  swap        65536MB SWAP
> mfid0s1f  <none>      10240MB *
> mfid0s1g  <none>        601GB *
> As you can see mfid0s1g is 601GB, and according to fstab that's /var.
> Yet df -h shows:
> # df -h
> Filesystem       Size    Used   Avail Capacity  Mounted on
> /dev/mfid0s1a    1.9G    726M    1.0G    41%    /
> devfs            1.0k    1.0k      0B   100%    /dev
> /dev/mfid0s1e    3.9G     38M    3.5G     1%    /home
> /dev/mfid0s1d     62G    6.6M     57G     0%    /tmp
> /dev/mfid0s1f    9.7G    7.5G    1.4G    84%    /usr
> /dev/mfid0s1g    582G     39G    496G     7%    /var
> So apparently I'm not creating this new slice?  It should be /dev/mfid0s1h,
> correct?

Let's not confuse slices (DOS partitions) with disklabels (BSD partitions).

DOS partitions are (maximum 4 per disk):


(according to your "fdisk -p" output, you're mfid0 disk is currently only using

BSD partitions are (maximum 8 per "slice" aka DOS partition):


(according to your sysinstall output, you're mfid0s1 slice has 5 BSD partitions
-- a, e, d, f, and g)

> How to I "recapture" the remaining 2+TB of space that's not being used?

The easiest way to use your extra space is to not adjust one of those 5 BSD
partitions, but instead create a new DOS partition (mfid0s2 as previously
discussed above). However, if you *really* want to "grow" an existing BSD
partition, this can be done (very carefully).

First, you'll want to save the output of "disklabel -r mfid0s1" to a text file.

Next, you'll have to re-fdisk mfid0 so that the first slice covers the entire
disk. Of course, re-mastering the slices does not affect the data, but it _will_
wipe out the BSD partition map (the disklabels; in other words, after using
fdisk to adjust the slice size of the first DOS partition, "disklabel -r
mfid0s1" will no longer return what it had before -- you'll have no disklabels
after), so the previous step of backing up the output of "disklabel -r ..." is

Next, you'll have to restore the disklabel (using "disklabel -e mfid0s1" and
cross-referencing your backup text file) with one slight adjustment...

You're going to use the *exact* values you backed up _EXCEPT_ you're going to
make the last label (position-wise -- taking care to note the byte ranges of
each disklabel -- ignoring "c" which of course is a pseudo label for "whole
slice") bigger while keeping the same offset (only the size of the last label
should change).

In your case, given the output you provided from sysinstall, this would likely
be your "g" label (but I'd have to see your "disklabel -r" output to know for
sure -- again, taking care to analyze the byte ranges).

Once you've re-written the disklabels (making sure to change nothing from your
previous backup except the size of the last label to cover the new unused
space), you're now at a position where you can "grow" the label with:

growfs /dev/mfid0s1g

NOTE: Should be done from a LiveFS (read: not while booted from said

That will zero out the unused inodes and make the new space available. Upon your
next boot you'll now have the new storage space available to your "g" label
(/var from the looks of it).

NOTE: If you wanted to change "g" to your "/usr" partition, rsync is your friend
-- while booted from a LiveFS like DruidBSD or mfsBSD etc.).

P.S. I take no responsibility for lost data -- caveat emptor.

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