gpart, bsdlabel and fdisk

[Aristedes Maniatis]

We are setting up a FreeBSD system from scratch and wanting to understand the new gpart utility. Our goal is to create a ZFS bootable install (mirror). In the past our approach has been to:

1. fdisk (allocate entire disk)
2. partition (1Gb UFS boot partition, swap and rest empty for ZFS)
3. set up ZFS [1]


Now we want to understand how to avoid the bootable UFS partition (which causes us some grief), but there is very little information about gpart as the tool to do it. I've found various guides (eg [2]) but am a little underwhelmed by the documentation, especially with magic commands like this as part of the set up:

echo 'a 1' | fdisk -f - /dev/ad4

It appears that gpart is largely replacing fdisk and bsdlabel.

* is this the future for FreeBSD and we should use gpart from here on? Are the old tools deprecated?

* we tried to reinstall the machine with some 7.2 CDs but the gparted disks caused fdisk to crash. Is this expected?

* is the result of using gpart completely different to the bsdlabel/fdisk we've known? Are the partitions on disk quite different?

* is there some source of good documentation out there other than the man page for gpart?

* has the MBR changed now with gpart?


Thanks

Ari Maniatis


[1] https://www.ish.com.au/solutions/articles/freebsdzfs
[2] http://outpost.h3q.com/patches/manageBE/create-FreeBSD-ZFS-bootfs.txt

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[Sean C. Farley-2]

On Wed, 21 Oct 2009, Aristedes Maniatis wrote:

> We are setting up a FreeBSD system from scratch and wanting to
> understand the new gpart utility. Our goal is to create a ZFS bootable
> install (mirror). In the past our approach has been to:
>
> 1. fdisk (allocate entire disk)
> 2. partition (1Gb UFS boot partition, swap and rest empty for ZFS)
> 3. set up ZFS [1]

*snip*

I will let others answer your specific questions.  However, I have a
file[1] that I have been writing to test installing a system with
gmirror using only gpart.  It may need tweaking and is a little overkill
(making room for a future install of Windows 7, if desired), but I can
use it to install successfully inside a VM.  The '-b 16' options are
important for the first partition within a slice to make room for the
metadata even though swap and UFS know to skip those bytes (thanks for
note from pjd about that).

The plan is to add this to my Wiki page at some point when I am ready.
If Windows is not involved, you could also try a GPT version of the
install instead of the MBR in the file, but this file should provide a
clue of what gpart can do.  I plan on making something equivalent for
gvinum next.

Comments and corrections welcome.

Sean
   1. http://people.freebsd.org/~scf/Install-gmirror.txt
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[Marcel Moolenaar-4]

On Oct 20, 2009, at 10:17 PM, Aristedes Maniatis wrote:
>
> * is this the future for FreeBSD and we should use gpart from here  
> on? Are the old tools deprecated?

Yes.

> * we tried to reinstall the machine with some 7.2 CDs but the  
> gparted disks caused fdisk to crash. Is this expected?

No, but that's because I don't know how buggy fdisk is.

> * is the result of using gpart completely different to the bsdlabel/
> fdisk we've known? Are the partitions on disk quite different?

The on-disk layout is dictated and cannot be different. As such,
they are the same.

> * is there some source of good documentation out there other than  
> the man page for gpart?

man gpart.

>
> * has the MBR changed now with gpart?

No.

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2009/10/22 Marcel Moolenaar <xcllnt@...>:
>
> On Oct 20, 2009, at 10:17 PM, Aristedes Maniatis wrote:

>> * is there some source of good documentation out there other than the man
>> page for gpart?
>
> man gpart.

I had to read the source. With respect, the man page for gpart(8) is
slightly misleading - it lists the -s and -b parameters to 'add' as
compulsory, and omits the 'interesting' (and useful) size suffix
decoding logic. I would post a patch, but I have no working FreeBSD
box for the next couple of weeks.

My NZD$0.02,
-James Butler
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[Aristedes Maniatis]

On 22/10/09 4:54 AM, Marcel Moolenaar wrote:

>> * is this the future for FreeBSD and we should use gpart from here
>> on? Are the old tools deprecated?
>
> Yes.

But the 8.0 sysinstall still uses fdisk and bsdlabel?


>> * is the result of using gpart completely different to the
>> bsdlabel/fdisk we've known? Are the partitions on disk quite different?
>
> The on-disk layout is dictated and cannot be different. As such,
> they are the same.

But some things look different. For example, old style labels were always of the style ad4s1b. But now the labels appear to be more flexible. Should we be using old style labels for compatibility with old tools, or does everything work with the new labelling options?

>> * is there some source of good documentation out there other than
>> the man page for gpart?
>
> man gpart.

Hmmm...  I was hoping for something more useful than that response. Where is it documented that I have to do "echo 'a 1' | fdisk -f - /dev/ad4" to make a disk bootable?


Is there a work-in-progress handbook page somewhere that describes the overall process of setting up disks with the new tools?


Ari Maniatis

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[Robert Noland]

On Thu, 2009-10-22 at 11:48 +1100, Aristedes Maniatis wrote:
> Hmmm...  I was hoping for something more useful than that response.
> Where is it documented that I have to do "echo 'a 1' | fdisk -f
> - /dev/ad4" to make a disk bootable?

I committed a patch the other day that will set the active flag for a
GPT partitioned disk when you install bootcode on it.

robert.

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[Aristedes Maniatis]

On 22/10/09 11:52 AM, Robert Noland wrote:
> On Thu, 2009-10-22 at 11:48 +1100, Aristedes Maniatis wrote:
>> >  Hmmm...  I was hoping for something more useful than that response.
>> >  Where is it documented that I have to do "echo 'a 1' | fdisk -f
>> >  - /dev/ad4" to make a disk bootable?

> I committed a patch the other day that will set the active flag for a
> GPT partitioned disk when you install bootcode on it.


Great. Will that make it to RC2?

Until then, is this the correct procedure to make a disk capable of booting ZFS:

   gpart bootcode -b /boot/boot0 ad4
   echo 'a 1' | fdisk -f - /dev/ad4

Sean mentions that 16 blocks have to be reserved at the start of the disk (to allow for the bootloader?). Will that also go away with your new patch so that the appropriate space is preserved? Will 16 blocks be enough forever?

Thanks

Ari

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[Robert Noland]

On Wed, 2009-10-21 at 16:17 +1100, Aristedes Maniatis wrote:
> We are setting up a FreeBSD system from scratch and wanting to understand the new gpart utility. Our goal is to create a ZFS bootable install (mirror). In the past our approach has been to:
>
> 1. fdisk (allocate entire disk)
> 2. partition (1Gb UFS boot partition, swap and rest empty for ZFS)
> 3. set up ZFS [1]

Make sure that your loader has zfs support.  Setting
LOADER_ZFS_SUPPORT="YES" in make.conf will take care of it.

gpart create -s GPT <disk>
gpart add -t freebsd-boot -s 128 <disk>
gpart add -t freebsd-swap -s XXX[mg] <disk>
gpart add -t freebsd-zfs <disk>
gpart bootcode -b /boot/pmbr -p /boot/gptzfsboot -i 1 <disk>
[I committed a patch that will set the active flag when you install
bootcode, but it is only in -CURRENT so far.

zpool create <pool> [mirror, raidz] <disk> <disk> ...

If you want more than a single root filesystem:

zfs create <filesystem>

You will need 3 other steps...

Now, install FreeBSD.

I generally bootstrap from a running system, so I just stick the disks
in and "make installworld DESTDIR=/pool && make installkernel
DESTDIR=/pool" followed by a "mergemaster -i -D /pool"

You need to install a cache in /boot/zfs/zpool.cache on the new
filesystem.  I generally do this by setting "zpool set
cachefile=/tmp/<poolname>.cache and then copying that
to /boot/zfs/zpool.cache.

After that, I usually set "zfs set mountpoint=legacy <pool>" which will
unmount the filesystem.

The gpart piece is really easy, once you get the hang of it...  Setting
up zfs root on a new machine is mostly tricky because you need to make
sure that you have a working loader.

robert.

> Now we want to understand how to avoid the bootable UFS partition (which causes us some grief), but there is very little information about gpart as the tool to do it. I've found various guides (eg [2]) but am a little underwhelmed by the documentation, especially with magic commands like this as part of the set up:
>
> echo 'a 1' | fdisk -f - /dev/ad4
>
> It appears that gpart is largely replacing fdisk and bsdlabel.
>
> * is this the future for FreeBSD and we should use gpart from here on? Are the old tools deprecated?
>
> * we tried to reinstall the machine with some 7.2 CDs but the gparted disks caused fdisk to crash. Is this expected?
>
> * is the result of using gpart completely different to the bsdlabel/fdisk we've known? Are the partitions on disk quite different?
>
> * is there some source of good documentation out there other than the man page for gpart?
>
> * has the MBR changed now with gpart?
>
>
> Thanks
>
> Ari Maniatis
>
>
> [1] https://www.ish.com.au/solutions/articles/freebsdzfs
> [2] http://outpost.h3q.com/patches/manageBE/create-FreeBSD-ZFS-bootfs.txt

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[Aristedes Maniatis]

On 22/10/09 12:16 PM, Robert Noland wrote:
> gpart create -s GPT<disk>

Sorry to keep asking so many questions, but hopefully this is all helpful to everyone else moving to the new gpart tools.

I can see there are three common partition types now in use on FreeBSD: MBR, BSD and GPT. I assume MBR is the same type sysinstall offerred FreeBSD users up until now for bootable disks. And GPT is the new type which is needed to support booting into ZFS. Does this explain why bsdlabel shows odd results for our GPT partitioned disks: it doesn't have support for GPT?

I don't understand this in the gpart manual:

    "The GEOM_PART_GPT option adds support for the GUID Partition Table (GPT) found on Intel Itanium computers and Intel-based Macintosh computers."

Why is GPT restricted to use on Macs and Itanium? As long as BIOS is able to load the boot sectors, shouldn't it work everywhere? Can you clarify this a little?

Will GPT be the default recommended partition type for all FreeBSD users now? Are there downsides to using it? Does it have a documentation page somewhere?

Thanks

Ari Maniatis

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[Robert Noland]

On Thu, 2009-10-22 at 12:15 +1100, Aristedes Maniatis wrote:

> On 22/10/09 11:52 AM, Robert Noland wrote:
> > On Thu, 2009-10-22 at 11:48 +1100, Aristedes Maniatis wrote:
> >> >  Hmmm...  I was hoping for something more useful than that response.
> >> >  Where is it documented that I have to do "echo 'a 1' | fdisk -f
> >> >  - /dev/ad4" to make a disk bootable?
>
> > I committed a patch the other day that will set the active flag for a
> > GPT partitioned disk when you install bootcode on it.
>
>
> Great. Will that make it to RC2?
>
> Until then, is this the correct procedure to make a disk capable of booting ZFS:
>
>    gpart bootcode -b /boot/boot0 ad4
>    echo 'a 1' | fdisk -f - /dev/ad4

I used to do it by just calling "fdisk -a /dev/ad4".  It prompts you and
did the right thing.  Note that only one of my machines needs the active
flag specifically set.  Most BIOS don't seem to need it, but then some
do and it doesn't hurt to set it.

> Sean mentions that 16 blocks have to be reserved at the start of the disk (to allow for the bootloader?). Will that also go away with your new patch so that the appropriate space is preserved? Will 16 blocks be enough forever?

I don't normally do this, no... But I'm not sure exactly how you have
setup your disks.  I use GPT and have not needed to do that... I posted
the procedure that I use a few minutes ago.

robert.
 
> Thanks
>
> Ari
>
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[Robert Noland]

On Thu, 2009-10-22 at 12:29 +1100, Aristedes Maniatis wrote:

> On 22/10/09 12:16 PM, Robert Noland wrote:
> > gpart create -s GPT<disk>
>
> Sorry to keep asking so many questions, but hopefully this is all helpful to everyone else moving to the new gpart tools.
>
> I can see there are three common partition types now in use on FreeBSD: MBR, BSD and GPT. I assume MBR is the same type sysinstall offerred FreeBSD users up until now for bootable disks. And GPT is the new type which is needed to support booting into ZFS. Does this explain why bsdlabel shows odd results for our GPT partitioned disks: it doesn't have support for GPT?
>
> I don't understand this in the gpart manual:
>
>     "The GEOM_PART_GPT option adds support for the GUID Partition Table (GPT) found on Intel Itanium computers and Intel-based Macintosh computers."
>
> Why is GPT restricted to use on Macs and Itanium? As long as BIOS is able to load the boot sectors, shouldn't it work everywhere? Can you clarify this a little?
>
> Will GPT be the default recommended partition type for all FreeBSD users now? Are there downsides to using it? Does it have a documentation page somewhere?

Well now... You probably want to wikipedia some of this....
http://en.wikipedia.org/wiki/Partition_%28computing%29 is probably a
good starting place.  GPT is the easiest way to get zfs working.  With
GPT you write a PMBR (protective master boot record) to sector 0 of the
drive.  This prevents (should prevent) older tools that don't understand
GPT from messing with the disk.  Basically it shows the disk as having a
single partition which encompasses the disk.  The GPT header then
occupies the second sector on the disk, followed by the partition
entries.

As I understand it (never actually tried it), Windows XP/Vista
whatever... Don't understand GPT yet, so you can't really dual boot with
it.  For that you probably still need an MBR scheme.  But I haven't run
into any pc systems that won't handle GPT yet, other than one of them
needing the active flag set in the PMBR.

robert.

> Thanks
>
> Ari Maniatis
>
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[Marcel Moolenaar-4]

On Oct 21, 2009, at 5:48 PM, Aristedes Maniatis wrote:

> On 22/10/09 4:54 AM, Marcel Moolenaar wrote:
>
>>> * is this the future for FreeBSD and we should use gpart from here
>>> on? Are the old tools deprecated?
>>
>> Yes.
>
> But the 8.0 sysinstall still uses fdisk and bsdlabel?

No, sysinstall has embedded code for partitioning.
It doesn't use fdisk, bsdlabel nor gpart.

>
>>> * is the result of using gpart completely different to the
>>> bsdlabel/fdisk we've known? Are the partitions on disk quite  
>>> different?
>>
>> The on-disk layout is dictated and cannot be different. As such,
>> they are the same.
>
> But some things look different. For example, old style labels were  
> always of the style ad4s1b.

ad4s1b means that ad4 has a MBR and in partition 4 of the MBR
is a BSD disklabel that has a 'b' partition. This is exactly
the same you get with gpart.

> But now the labels appear to be more flexible. Should we be using  
> old style labels for compatibility with old tools, or does  
> everything work with the new labelling options?

There's not really an old style or a new style. gpart (with
GEOM_PART in the kernel) is just a different way of creating
on-disk partitions. gpart does add some flexibility in some
cases (more than 8 partitions in the BSD disklabel), but it's
still a BSD disklabel.

>
>>> * is there some source of good documentation out there other than
>>> the man page for gpart?
>>
>> man gpart.
>
> Hmmm...  I was hoping for something more useful than that response.  
> Where is it documented that I have to do "echo 'a 1' | fdisk -f - /
> dev/ad4" to make a disk bootable?

man fdisk :-)

Or with gpart:

# gpart set -a active -i 1 ad4


> Is there a work-in-progress handbook page somewhere that describes  
> the overall process of setting up disks with the new tools?

It typically takes a while for that to catch up with
events. I don't think there's a WIP just yet...

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[Aristedes Maniatis]

On 22/10/09 12:16 PM, Robert Noland wrote:
> Make sure that your loader has zfs support.  Setting
> LOADER_ZFS_SUPPORT="YES" in make.conf will take care of it.

Does this setting just create /boot/pmbr and /boot/gptzfsboot files in /boot? We use freebsd-update as a binary update mechanism and I can see those files already exist (8.0-RC1), so perhaps it isn't needed except to compile the appropriate boot loader files?

Also, LOADER_ZFS_SUPPORT does not appear in the man page for make.conf.

Once I have everything figured out, I'll write up a blog post with a set of instructions on what I've learnt. Hopefully that will help others in the future.

Thanks

Ari Maniatis

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[Robert Noland]

On Wed, 2009-10-21 at 19:45 -0700, Marcel Moolenaar wrote:
> # gpart set -a active -i 1 ad4

FWIW, this does not work on GPT schemes... Which is a key reason that I
patched the bootcode option for GPT schemes.

robert.

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[Robert Noland]

On Thu, 2009-10-22 at 14:22 +1100, Aristedes Maniatis wrote:
> On 22/10/09 12:16 PM, Robert Noland wrote:
> > Make sure that your loader has zfs support.  Setting
> > LOADER_ZFS_SUPPORT="YES" in make.conf will take care of it.
>
> Does this setting just create /boot/pmbr and /boot/gptzfsboot files in /boot? We use freebsd-update as a binary update mechanism and I can see those files already exist (8.0-RC1), so perhaps it isn't needed except to compile the appropriate boot loader files?

gptboot and pmbr should be there always... The LOADER_ZFS_SUPPORT has to
do with it requiring CDDL code and so isn't / wasn't built by default...
I'm not fully aware of the details... I just know that when I setup my
first amd64 box w/ zfs root it wasn't part of the normal CDs.  So I
built up a temporary install to bootstrap it and install the OS.

robert.

> Also, LOADER_ZFS_SUPPORT does not appear in the man page for make.conf.
>
> Once I have everything figured out, I'll write up a blog post with a set of instructions on what I've learnt. Hopefully that will help others in the future.
>
> Thanks
>
> Ari Maniatis
>
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[Scot Hetzel]

On Wed, Oct 21, 2009 at 10:22 PM, Aristedes Maniatis <ari@...> wrote:

> On 22/10/09 12:16 PM, Robert Noland wrote:
>>
>> Make sure that your loader has zfs support.  Setting
>> LOADER_ZFS_SUPPORT="YES" in make.conf will take care of it.
>
> Does this setting just create /boot/pmbr and /boot/gptzfsboot files in
> /boot? We use freebsd-update as a binary update mechanism and I can see
> those files already exist (8.0-RC1), so perhaps it isn't needed except to
> compile the appropriate boot loader files?
>
> Also, LOADER_ZFS_SUPPORT does not appear in the man page for make.conf.
>
> Once I have everything figured out, I'll write up a blog post with a set of
> instructions on what I've learnt. Hopefully that will help others in the
> future.
>

You may also want to check out these pages I created on how to setup a
Root on ZFS configuration with ZFS using MBR, and GPT (Single, Mirror,
RAIDZ1, RAIDZ2) Configurations.

http://wiki.freebsd.org/RootOnZFS

If anyone notices a problem with them, either let me know or update
the wiki page.

Scot
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[Aristedes Maniatis]

On 22/10/09 6:01 PM, Scot Hetzel wrote:
> http://wiki.freebsd.org/RootOnZFS
>
> If anyone notices a problem with them, either let me know or update
> the wiki page.

That's very helpful, thanks Scot. It raises some questions:

* you don't have the instruction to perform "echo 'a 1' | fdisk -f - /dev/ad4" which Robert recommends

* Robert recommends GPT as the "easiest way to get ZFS on root working". Your instructions seem to lean more toward MBR "The advantage of using a MBR disk is that you can still dual boot with other Operating Systems.". Are there any downsides of using MBR which should be explained?

* I've seen posts here (sorry I don't have one handy) which recommend to not put swap on ZFS. Apart from crash dumps are there any other reasons to prefer one over the other? Your instructions explain both, without giving much of a guide about why you'd choose one. Is a 'native' swap faster than one on ZFS?

* you write LOADER_ZFS_SUPPORT=YES to src.conf, while previous instruction in this thread had it written to make.conf

* In order to follow http://wiki.freebsd.org/RootOnZFS/GPTZFSBoot/Mirror will you need to run this from the live CD rather than the first install CD?

* At the top of the same page you give instructions for creating boot, swap and zfs partitions. But your instructions give block sizes very specific to your disks. It would be helpful to have something like:

   gpart add -b 34 -s 128 -t freebsd-boot ad0   (why 34? this is a different magic number to other magic numbers I've seen suggested)
   gpart add -b 162 -s 8G -t freebsd-swap ad0   (the 8G is more readable than specifying in sectors)

or even

   gpart add -b 162 -s 8G -t freebsd-swap -l swap-ad0 ad0  (the human readable label appears to be a nice feature of GPT)

then

   gpart show ad0
   
   and look for the offset and size following the "free" space.  [1]

   offset=`gpart show ad0 | grep '\- free \-' | awk '{print $1}'`
   size=`gpart show ad0 | grep '\- free \-' | awk '{print $2}'`

   gpart add -b $offset -s $size -t freebsd-zfs -l system-ad0 ad0


As a feature request it would be great if gpart supported "-s all" and made "-b" optional so that the next add starts at the beginning of the first free space.

Ari



[1] That's from Philipp Wuensche's instructions I found.

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[Thomas Backman]

On Oct 22, 2009, at 10:09 AM, Aristedes Maniatis wrote:

> On 22/10/09 6:01 PM, Scot Hetzel wrote:
>> http://wiki.freebsd.org/RootOnZFS
>>
>> If anyone notices a problem with them, either let me know or update
>> the wiki page.
>
> That's very helpful, thanks Scot. It raises some questions:
>
> * you don't have the instruction to perform "echo 'a 1' | fdisk -f  
> - /dev/ad4" which Robert recommends

Shouldn't be needed if you use gpart. (Note: I haven't actually read  
the guides, but fdisk and gpart are both partitioning software, and I  
don't see why you'd need *both*. I've made several installs without  
ever touching fdisk, all ZFS only.)
>
> * Robert recommends GPT as the "easiest way to get ZFS on root  
> working". Your instructions seem to lean more toward MBR "The  
> advantage of using a MBR disk is that you can still dual boot with  
> other Operating Systems.". Are there any downsides of using MBR  
> which should be explained?
The biggest downside is the 2TB partition limit, both in size and  
offset. Larger disks (including HW RAID arrays) and you can't use MBR  
(without wasting space, of course).
>
> * you write LOADER_ZFS_SUPPORT=YES to src.conf, while previous  
> instruction in this thread had it written to make.conf
Doesn't matter, both are used for /usr/src; ports however doesn't read  
src.conf.

> As a feature request it would be great if gpart supported "-s all"  
> and made "-b" optional so that the next add starts at the beginning  
> of the first free space.
It's already supported, swap the last command for e.g.:
gpart add -t freebsd-zfs ad0 # Automatically fills the rest of the  
disk with a partition starting at the first free offset

Regards,
Thomas
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[Robert Noland]

On Thu, 2009-10-22 at 10:15 +0200, Thomas Backman wrote:
> > * you don't have the instruction to perform "echo 'a 1' | fdisk -f  
> > - /dev/ad4" which Robert recommends
> Shouldn't be needed if you use gpart. (Note: I haven't actually read  
> the guides, but fdisk and gpart are both partitioning software, and
> I  
> don't see why you'd need *both*. I've made several installs without  
> ever touching fdisk, all ZFS only.)

This step is only needed if you BIOS requires it.  Many/Most do not.  It
is set automatically when you install bootcode to a GPT partitioned disk
on -CURRENT now.

robert.

--
Robert Noland <rnoland@...>
FreeBSD

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[xSAPPYx]

On Wed, Oct 21, 2009 at 6:29 PM, Aristedes Maniatis <ari@...> wrote:
> On 22/10/09 12:16 PM, Robert Noland wrote:
> I don't understand this in the gpart manual:
>
>   "The GEOM_PART_GPT option adds support for the GUID Partition Table (GPT)
> found on Intel Itanium computers and Intel-based Macintosh computers."
>
> Why is GPT restricted to use on Macs and Itanium? As long as BIOS is able to
> load the boot sectors, shouldn't it work everywhere? Can you clarify this a
> little?

As I understand it, Macs and Itanium were just the first adopters of
EFI, the new boot method to take over the old school bios / mbr
system.
GPT is the disk partition part of EFI:
http://en.wikipedia.org/wiki/GUID_Partition_Table
We are in the transition period between the two, with gpt being the future.
IIRC there is a 2TB limit for mbr partitioned disks... we will all be
running gpt soon enough
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