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Date:      Thu, 5 Feb 2009 17:23:26 -0500
From:      Jerry McAllister <>
To:        perikillo <>
Cc:        FreeBSD Mailing List <>
Subject:   Re: Shrink a Slice? FreeBSD 7.1
Message-ID:  <>
In-Reply-To: <>
References:  <>

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On Thu, Feb 05, 2009 at 12:19:13PM -0800, perikillo wrote:

>    Hi people.
>    I have been googling without any good info about: How to shrink a slice?
>    Case: I installed a new server for mysql, is working, I already install
> all the ports I need, them I spend a lot of hours yesterday with this baby,
> now this is my current disk layout:
> /dev/ad0s1a on / (ufs, local, noatime, soft-updates)
> devfs on /dev (devfs, local)
> /dev/ad0s1f on /tmp (ufs, local, noatime, soft-updates)
> /dev/ad0s1d on /usr (ufs, local, noatime, soft-updates)
> /dev/ad0s1e on /var (ufs, local, noatime, soft-updates)
> /dev/ad0s1g on /backups (ufs, local, soft-updates)
>    What I want to do is to shrink the slice /dev/ad0s1g

  /dev/ad0s1g is a partition, not a slice.
  /dev/ad0s1 is the slice.

MicroSloth usage of the terms is different and confuses people sometimes.

As far as I know neither growfs(8) nor tunefs(8) can shrink the disk
allocated to a partition.

The only way is to dump each of the filesystems to some other
reliable media (maybe tape or a large USB disk) and then repartition
that slice to be the sizes you want.    Use dump(8) to make the dumps
and then check the dump files out before starting the repartitioning.

First you have to build a filesystem on the USB drive.   
You should be able to use bsdlabel to create a single partition
that covers the whole drive.   

But, if your FreeBSD or BIOS is old enough it might not go that big, 
so you will need to break it down in to smaller slices and make a 
partition in each.  (I have had to do that.  But if it is 7.xx it 
should not be necessary)  To break it up, get the  gparted  utility.   
Download its boot image and use it to break up the USB disk in to 
slices that your FreeBSD will handle.  You need to have it make all 
what it calls (in the MS way) Primary Partitions, but those are what 
are called slices in FreeBSD land.

Don't get tempted to use gparted to shrink your ad0s1 slice because
it will not work right.   That will just trash the current partitions.
It is not what you are looking for.

Either if your FreeBSD will handle the whole USB or after you have it
broken up, then build a partition on each slice of the USB using bsdlabel.
Don't make it bootable or write a boot sector on it.  Then run newfs(8)
on it to make a filesystem.
This bsdlabel and newfs can be done while the system is running.

Then, take the system down and run the dumps.    You can do the dumps
from single user mode or boot a fixit image from the install CD.
You will need to do the repartitioning and restore the dumps from
the fixit anyway so you could just start there.
Boot the machine from the fixit disk - create a 'holographic' image as 
they call it.   Fixit is usually on disc1.

Run the dumps.
Lets say you are doing the dumps to a USB drive that comes up
as /dev/da0 in the fixit boot and your current disk still is
comes up with the name  /dev/ad0 .

First, make up mount points for all your filesystems that you want to
dump plus for the filesystem[s] on the USB drive.
NOTE: That the fixit runs from a memory resident filesystem so whatever
      you create there will disappear on boot.

Anyway, skip dumping /tmp and /dev is a pretend filesystem.

mkdir /oldroot
mkdir /oldusr
mkdir /oldvar
mkdir /oldbkup

mkdir /usbdrive

(You can actually make the dumps from the devices rather than mounting 
 them, but I have never gotten in to that habit)

Mount those partitions

mount /dev/ad0s1a /oldroot
mount /dev/ad0s1d /oldusr
mount /dev/ad0s1e /oldvar
mount /dev/ad0s1g /oldbkup

mount /dev/da0s1 /usbdrive    (This device name might be different
depending on how you make it.   Some possibilities are:
      /dev/da0s1    If you just newfs the slice without making a partition in it
      /dev/da0s1a  If you make a slice with fdisk and a partition with bsdlabel
      /dev/da0a    If you make a partition with bsdlabel without making a slice

Now do the dumps

dump 0af /usbdrive/rootdump /oldroot
dump 0af /usbdrive/usrdump /oldusr
dump 0af /usbdrive/vardump /oldvar
dump 0af /usbdrive/bkupdump /oldbkup

This will take a while depending on media you use.
By the way, to tape it would go to /dev/nsa0 rather than /usbdrive/oldroot, etc

Once the dumps are done, you may want to reboot and mount that USB
drive or read the tape and look at the dumps to make sure they can
be read.     Just a precaution.

At least you will need to unmount all the partitions so bsdlabel
can work on them

Anyway, once you are happy with your dumps, then get back in to
the fixit and use bsdlabel to rewrite the partitions.

Just bsdlabel -e ad0s1

(You should not need to write a new boot block as this process should
 not touch that sector)

Adjust the partitions as you see fit.   Make partition 'a' start 
at offset of 0  and use a '*' for the rest of the offsets.
bsdlabel will calculate them correctly.  You can also make the 
size of the last partition be '*' and bsdlabel will put the remainder
of the usable space in it.

Write/Quit out of the bsdlabel editor  -- just like vi.

Now you need to do a newfs for each partition except for swap.

Just take the defaults.   Do:

newfs /dev/ad0s1a
newfs /dev/ad0s1d
newfs /dev/ad0s1e  
  etc for how many you made.

Once that is done, you need to mount up the partitions
and restore the dumps.
Remember that if you rebooted the fixit from when you first
made the mount points, you will have to make them again and
remount things.

Restores will look like:

cd /oldroot 
restore -rf /usbdrive/rootdump
cd /oldusr
restore -rf /usbdrive/usrdump
cd /oldvar
restore -rf /usbdrive/vardump
cd /oldbkup
restore -rf /usbdrive/bkupdump

If you created a new partition while doing this, there is currently
nothing to put in it.   You will need to reboot and then you can
split things up and move data as you see fit.


> Filesystem  1M-blocks   Used  Avail Capacity  Mounted on
> /dev/ad0s1a       495    232    223    51%    /
> devfs               0      0      0   100%    /dev
> /dev/ad0s1f       495      0    456     0%    /tmp
> /dev/ad0s1d      5967   4225   1264    77%    /usr
> /dev/ad0s1e     15863   1343  13251     9%    /var
> /dev/ad0s1g    272313  48823 201704    19%    /backups
>   Like u can see, is the last slice I have, is posible to remove that slice
> and create a new one?
>   I don't have info there yet and is not a freebsd default slice, I know
> that I need to umount first.
>   I have been reading some post but all I have seen is that ins not possible
> or I'm wrong?
>   I try to with sysinstall looks like don't let me do this.
>   Running FreeBSD 7.1-p2.
>   Thanks all for your time!!!
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