Partitioning a RAID device

Partitioning a RAID device

[Arne Wiebalck]

Hello,

is it possible to have partitions on a RAID device?

I tried to use fdisk/cfdisk for that. I could set up partitions named
md0p1, md0p2 and so on. The names were given automatically by the tools.

After quit and restart, cfdisk showed the partitions I just set up.
But the corresponding special files were missing, so I created
them using mknod.

After a reboot, cfdisk still reported the partitions to be on the RAID
device, but whenever I try to run a mke2fs, it reports

mke2fs: Device size reported to be zero.  Invalid partition specified, or
        partition table wasn't reread after running fdisk, due to
        a modified partition being busy and in use.  You may need to
        reboot to re-read your partition table.

Anything I am missing here?

TIA,

 arne




**********************************************************************
 Arne Wiebalck                        Kirchhoff Institute for Physics
                                           Technical Computer Science
                                                     Schroederstr. 90
                                                   D-69120 Heidelberg

 e-mail: wiebalck@kip.uni-heidelberg.de      Tel.: (+49) 6221/54-4362
 web   : http://www.kip.uni-heidelberg.de    Fax.: (+49) 6221/54-4345
**********************************************************************

Re: Partitioning a RAID device

[Derek Vadala]

On Wed, 4 Sep 2002, Arne Wiebalck wrote:

> is it possible to have partitions on a RAID device?
>
> [...]
>
> Anything I am missing here?

You first need to patch your kernel so that the md driver and md devices
support partitioning. Check out
http://cgi.cse.unsw.edu.au/~neilb/patches/linux-stable/ for the patches.


---
Derek Vadala, derek@cynicism.com, http://www.cynicism.com/~derek

Re: Partitioning a RAID device

[Michael Tokarev]

Derek Vadala wrote:
> 
> On Wed, 4 Sep 2002, Arne Wiebalck wrote:
> 
> > is it possible to have partitions on a RAID device?
> >
> > [...]
> >
> > Anything I am missing here?
> 
> You first need to patch your kernel so that the md driver and md devices
> support partitioning. Check out
> http://cgi.cse.unsw.edu.au/~neilb/patches/linux-stable/ for the patches.

Hmm, interesting.  What's those patches are for?  What's their status?
Are they just experiments, proof-of-concept, or intended for general
use?  Are there any interdependances of the set of 5 md-related patches
for 2.4.19?  Some more information on this all?  Discussions?  Official
2.4/2.5 status of this work?  Relation with e.g. LVM?  Iteraction with
devfs for mdp?  Device nodes assignment (i.e. what will become mpa, mpb
etc when one have md0, md1 etc)?  (There are quite a few aspects mentioned
on the above page, mostly nfs-, ext[23]- and md-related stuff, but this is
linux-raid list :)

Errm, so many question... ;)

BTW, still don't know which is "better" -- have several md arrays for every
filesystem/whatether, or have one md array and split it using e.g. lvm or
using this mdp method?  (Two different point of view: system resource usage
should be less for one large md array, but will this one large array handle
load as effective as several independant ones?)

Thanks.

/mjt

Re: Partitioning a RAID device

[Arne Wiebalck]

thanks for the hint!
I applied all the md patches for my kernel (2.4.18).

the compilation complained about __minor not to be member of the
mddev structure, so replaced it by a __unit. apart from that patching and
compiling was without problems.

I tried to partition the device using fdisk, but in /var/log/messages
I found

fdisk(pid 1344) tried BLKRRPART ioctl on MD device. Should use MDP device.

and

md: fdisk(pid 2486) used obsolete MD ioctl, upgrade your software to use
new ictls.

so, partitioning did not work.

my fdisk version is 2.11.
should I use another tool for partitioning?
who is responsible for making the device special files?

TIA,
 arne



On Wed, 4 Sep 2002, Derek Vadala wrote:

> On Wed, 4 Sep 2002, Arne Wiebalck wrote:
>
> > is it possible to have partitions on a RAID device?
> >
> > [...]
> >
> > Anything I am missing here?
>
> You first need to patch your kernel so that the md driver and md devices
> support partitioning. Check out
> http://cgi.cse.unsw.edu.au/~neilb/patches/linux-stable/ for the patches.
>
>
> ---
> Derek Vadala, derek@cynicism.com, http://www.cynicism.com/~derek
>

**********************************************************************
 Arne Wiebalck                        Kirchhoff Institute for Physics
                                           Technical Computer Science
                                                     Schroederstr. 90
                                                   D-69120 Heidelberg

 e-mail: wiebalck@kip.uni-heidelberg.de      Tel.: (+49) 6221/54-4362
 web   : http://www.kip.uni-heidelberg.de    Fax.: (+49) 6221/54-4345
**********************************************************************

Re: Partitioning a RAID device

[Neil Brown]

On Thursday September 5, wiebalck@kip.uni-heidelberg.de wrote:
> 
> fdisk(pid 1344) tried BLKRRPART ioctl on MD device. Should use MDP
> device.

Yes, you shold use the MDP devices... look in /proc/devices to find
the major number.
> 
> md: fdisk(pid 2486) used obsolete MD ioctl, upgrade your software to use
> new ictls.

Ignore this, it doesn't really mean anything.

> 
> so, partitioning did not work.
> 
> my fdisk version is 2.11.
> should I use another tool for partitioning?

fdisk, cfdisk, sfdisk all work fine.

> who is responsible for making the device special files?

You.  (or devfs).
The first 16 minors for mdp correspond to md0
The second 16 minors for mdp correspond to md1
etc.

NeilBrown

Re: Partitioning a RAID device

[Neil Brown]

On Thursday September 5, mjt@tls.msk.ru wrote:
> Derek Vadala wrote:
> > 
> > On Wed, 4 Sep 2002, Arne Wiebalck wrote:
> > 
> > > is it possible to have partitions on a RAID device?
> > >
> > > [...]
> > >
> > > Anything I am missing here?
> > 
> > You first need to patch your kernel so that the md driver and md devices
> > support partitioning. Check out
> > http://cgi.cse.unsw.edu.au/~neilb/patches/linux-stable/ for the patches.
> 
> Hmm, interesting.  What's those patches are for?  What's their status?
> Are they just experiments, proof-of-concept, or intended for general
> use?  Are there any interdependances of the set of 5 md-related patches
> for 2.4.19?  Some more information on this all?  Discussions?  Official
> 2.4/2.5 status of this work?  Relation with e.g. LVM?  Iteraction with
> devfs for mdp?  Device nodes assignment (i.e. what will become mpa, mpb
> etc when one have md0, md1 etc)?  (There are quite a few aspects mentioned
> on the above page, mostly nfs-, ext[23]- and md-related stuff, but this is
> linux-raid list :)
> 
> Errm, so many question... ;)

State:  I use them in production on most of my servers.
I like to mirror two whole devices together, and use that as the
system disk.  I parition it for a root,  a swap, and an other-stuff
partitions.

Lilo needs a bit of coaxing to make it work with partitioned raid.

Dependancies: probably.  I should sort them out and maybe submit bits
to Marcelo if I ever find a minute.  I'd kind-of like to ge
partitioning into 2.5 before I submit it for 2.4 though.

LVM:  Independant, thought can provide vaguely similar function.

devfs: works fine. try it and see.

device nodes:
  minors 0..15 are
   /dev/md/d0, /dev/md/d0p1, /dev/md/d0p2, ... /dev/md/d0p15
  minors 16..31 are
   /dev/md/d1, /dev/md/d1p1, /dev/md/d1p2, ... /dev/md/d1p15

 /dev/md/d0 is the same as /dev/md0
 /dev/md/d1 is the same as /dev/md1

> 
> BTW, still don't know which is "better" -- have several md arrays for every
> filesystem/whatether, or have one md array and split it using e.g. lvm or
> using this mdp method?  (Two different point of view: system resource usage
> should be less for one large md array, but will this one large array handle
> load as effective as several independant ones?)

Depends what you want to do.  As I said, I use a partitions raid1 part
of drives for some servers.  
For others (where I want a bit more disk space and so have extra
drives) I partition each drive, into root, swap and rest.
All the roots are raid1 together.
All the swaps are raid1 together
All the rest are raid5 together.

NeilBrown

Re: Partitioning a RAID device

[Arne Wiebalck]

ok, works fine. thanks for your help.

arne


On Fri, 6 Sep 2002, Neil Brown wrote:

> On Thursday September 5, wiebalck@kip.uni-heidelberg.de wrote:
> >
> > fdisk(pid 1344) tried BLKRRPART ioctl on MD device. Should use MDP
> > device.
>
> Yes, you shold use the MDP devices... look in /proc/devices to find
> the major number.
> >
> > md: fdisk(pid 2486) used obsolete MD ioctl, upgrade your software to use
> > new ictls.
>
> Ignore this, it doesn't really mean anything.
>
> >
> > so, partitioning did not work.
> >
> > my fdisk version is 2.11.
> > should I use another tool for partitioning?
>
> fdisk, cfdisk, sfdisk all work fine.
>
> > who is responsible for making the device special files?
>
> You.  (or devfs).
> The first 16 minors for mdp correspond to md0
> The second 16 minors for mdp correspond to md1
> etc.
>
> NeilBrown
> -
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>

**********************************************************************
 Arne Wiebalck                        Kirchhoff Institute for Physics
                                           Technical Computer Science
                                                     Schroederstr. 90
                                                   D-69120 Heidelberg

 e-mail: wiebalck@kip.uni-heidelberg.de      Tel.: (+49) 6221/54-4362
 web   : http://www.kip.uni-heidelberg.de    Fax.: (+49) 6221/54-4345
**********************************************************************