Xen users - Feb 2009 - propagating blktap partition changes

Hi,

I have 2 questions:

 1. I was not able to let the guest know that the partition size was changed.
 2. I was not able to use block-attach with the same backendfile to different 
machines (eg: guest + dom0)

I''ve read that block-reconfigure could''ve been used for this,
except that it
wasn''t designed to work for filebased vbd on PVs, only for switching
CDROMs
in HVM

When you use a local disk on a machine, you can use fdisk to change partitions 
and sizes, it then rereads the partition table to reflect those changes.

Since i''m not using a disk, but directly partitions, isn''t it
possible to just
give a signal to the guest that it should recheck the partition? can be from 
the guest itself.

Some kind of workaround?

Sincerely,

Maarten

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On Thu, Feb 05, 2009 at 11:52:56AM +0100, Maarten Vanraes
wrote:
> Hi,
> 
> I have 2 questions:
> 
>  1. I was not able to let the guest know that the partition size was
changed.
>  2. I was not able to use block-attach with the same backendfile to
different
> machines (eg: guest + dom0)
> 
> I''ve read that block-reconfigure could''ve been used for
this, except that it
> wasn''t designed to work for filebased vbd on PVs, only for
switching CDROMs
> in HVM
> 
> When you use a local disk on a machine, you can use fdisk to change
partitions
> and sizes, it then rereads the partition table to reflect those changes.
> 
> Since i''m not using a disk, but directly partitions,
isn''t it possible to just
> give a signal to the guest that it should recheck the partition? can be
from
> the guest itself.
> 
> Some kind of workaround?
> 
Sorry, this is not possible.

There''s a a feature request about it for Xen 3.4. 

Dunno if it will be implemented.

-- Pasi

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Op Thursday 05 February 2009 13:05:01 schreef Pasi
Kärkkäinen:
> On Thu, Feb 05, 2009 at 11:52:56AM +0100, Maarten Vanraes wrote:
> > Hi,
> >
> > I have 2 questions:
> >
> >  1. I was not able to let the guest know that the partition size was
> > changed. 2. I was not able to use block-attach with the same
backendfile
> > to different machines (eg: guest + dom0)
> >
> > I''ve read that block-reconfigure could''ve been used
for this, except that
> > it wasn''t designed to work for filebased vbd on PVs, only for
switching
> > CDROMs in HVM
> >
> > When you use a local disk on a machine, you can use fdisk to change
> > partitions and sizes, it then rereads the partition table to reflect
> > those changes.
> >
> > Since i''m not using a disk, but directly partitions,
isn''t it possible to
> > just give a signal to the guest that it should recheck the partition?
can
> > be from the guest itself.
> >
> > Some kind of workaround?
>
> Sorry, this is not possible.
>
> There''s a a feature request about it for Xen 3.4.
>
> Dunno if it will be implemented.
>
> -- Pasi
Yes, i read your thread, i was hoping for some kind of workaround, some kind 
of "thing" i can execute on the guest, that would make the kernel
recheck
it''s partition size or something.

Maarten

_______________________________________________
Xen-users mailing list
Xen-users@lists.xensource.com
http://lists.xensource.com/xen-users

On Thu, Feb 05, 2009 at 01:59:57PM +0100, Maarten Vanraes
wrote:
> Op Thursday 05 February 2009 13:05:01 schreef Pasi Kärkkäinen:
> > On Thu, Feb 05, 2009 at 11:52:56AM +0100, Maarten Vanraes wrote:
> > > Hi,
> > >
> > > I have 2 questions:
> > >
> > >  1. I was not able to let the guest know that the partition size
was
> > > changed. 2. I was not able to use block-attach with the same
backendfile
> > > to different machines (eg: guest + dom0)
> > >
> > > I''ve read that block-reconfigure could''ve been
used for this, except that
> > > it wasn''t designed to work for filebased vbd on PVs,
only for switching
> > > CDROMs in HVM
> > >
> > > When you use a local disk on a machine, you can use fdisk to
change
> > > partitions and sizes, it then rereads the partition table to
reflect
> > > those changes.
> > >
> > > Since i''m not using a disk, but directly partitions,
isn''t it possible to
> > > just give a signal to the guest that it should recheck the
partition? can
> > > be from the guest itself.
> > >
> > > Some kind of workaround?
> >
> > Sorry, this is not possible.
> >
> > There''s a a feature request about it for Xen 3.4.
> >
> > Dunno if it will be implemented.
> >
> > -- Pasi
> 
> Yes, i read your thread, i was hoping for some kind of workaround, some
kind
> of "thing" i can execute on the guest, that would make the kernel
recheck
> it''s partition size or something.
> 
The problem is not about rereading the partition table; this can be done
using for example "blockdev --rereadpt".

The problem is to get the disk device (/dev/xvd*) resized.. ie. getting the
kernel to see
the DISK has been resized. 

After the disk has been resized, partition table can be resized after that. 

Disk resizing on the fly is not supported today with Xen.

-- Pasi

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Xen-users mailing list
Xen-users@lists.xensource.com
http://lists.xensource.com/xen-users

Op Thursday 05 February 2009 15:27:55 schreef Pasi
Kärkkäinen:
> On Thu, Feb 05, 2009 at 01:59:57PM +0100, Maarten Vanraes wrote:
> > Op Thursday 05 February 2009 13:05:01 schreef Pasi Kärkkäinen:
> > > On Thu, Feb 05, 2009 at 11:52:56AM +0100, Maarten Vanraes wrote:
> > > > Hi,
> > > >
> > > > I have 2 questions:
> > > >
> > > >  1. I was not able to let the guest know that the partition
size was
> > > > changed. 2. I was not able to use block-attach with the same
> > > > backendfile to different machines (eg: guest + dom0)
> > > >
> > > > I''ve read that block-reconfigure could''ve
been used for this, except
> > > > that it wasn''t designed to work for filebased vbd
on PVs, only for
> > > > switching CDROMs in HVM
> > > >
> > > > When you use a local disk on a machine, you can use fdisk to
change
> > > > partitions and sizes, it then rereads the partition table to
reflect
> > > > those changes.
> > > >
> > > > Since i''m not using a disk, but directly
partitions, isn''t it
> > > > possible to just give a signal to the guest that it should
recheck
> > > > the partition? can be from the guest itself.
> > > >
> > > > Some kind of workaround?
> > >
> > > Sorry, this is not possible.
> > >
> > > There''s a a feature request about it for Xen 3.4.
> > >
> > > Dunno if it will be implemented.
> > >
> > > -- Pasi
> >
> > Yes, i read your thread, i was hoping for some kind of workaround,
some
> > kind of "thing" i can execute on the guest, that would make
the kernel
> > recheck it''s partition size or something.
>
> The problem is not about rereading the partition table; this can be done
> using for example "blockdev --rereadpt".
>
> The problem is to get the disk device (/dev/xvd*) resized.. ie. getting the
> kernel to see the DISK has been resized.
>
> After the disk has been resized, partition table can be resized after that.
>
> Disk resizing on the fly is not supported today with Xen.
Well I understand that it is inside the kernel, but, i''m not using
disks, i''m
using partitions directly:

e.g.:

''tap:aio:/opt/data/file.img, sda1, w''

I can make the partition file larger on dom0 no problem, i could even resize 
the partition live on dom0 no problem.

But (i guess the kernel) doesn''t see the partition as larger, even with
forced
operations, i still get read errors at the end.

I''m not even sure the blktap device detected this change in size on
dom0.

But if i''m using directly partitions, maybe there is some code that i
can
execute that does kernel calls or something to refresh it''s device. ie:
a
workaround.

I mean, hotplug seems to be able to do it just fine. ie: memory is detected as 
larger, i imagine there is such code for block devices as well, no? So i 
figured there should be something i can do in the guest (maybe even on kernel 
level) that could force the re-detection of the device or something.

Of course if blktap can''t even pass on the information to the guest,
this
would not work at all...

Sincerely,

Maarten

_______________________________________________
Xen-users mailing list
Xen-users@lists.xensource.com
http://lists.xensource.com/xen-users

On Thu, Feb 05, 2009 at 03:35:18PM +0100, Maarten Vanraes
wrote:
> Op Thursday 05 February 2009 15:27:55 schreef Pasi Kärkkäinen:
> > On Thu, Feb 05, 2009 at 01:59:57PM +0100, Maarten Vanraes wrote:
> > > Op Thursday 05 February 2009 13:05:01 schreef Pasi Kärkkäinen:
> > > > On Thu, Feb 05, 2009 at 11:52:56AM +0100, Maarten Vanraes
wrote:
> > > > > Hi,
> > > > >
> > > > > I have 2 questions:
> > > > >
> > > > >  1. I was not able to let the guest know that the
partition size was
> > > > > changed. 2. I was not able to use block-attach with the
same
> > > > > backendfile to different machines (eg: guest + dom0)
> > > > >
> > > > > I''ve read that block-reconfigure
could''ve been used for this, except
> > > > > that it wasn''t designed to work for filebased
vbd on PVs, only for
> > > > > switching CDROMs in HVM
> > > > >
> > > > > When you use a local disk on a machine, you can use
fdisk to change
> > > > > partitions and sizes, it then rereads the partition
table to reflect
> > > > > those changes.
> > > > >
> > > > > Since i''m not using a disk, but directly
partitions, isn''t it
> > > > > possible to just give a signal to the guest that it
should recheck
> > > > > the partition? can be from the guest itself.
> > > > >
> > > > > Some kind of workaround?
> > > >
> > > > Sorry, this is not possible.
> > > >
> > > > There''s a a feature request about it for Xen 3.4.
> > > >
> > > > Dunno if it will be implemented.
> > > >
> > > > -- Pasi
> > >
> > > Yes, i read your thread, i was hoping for some kind of
workaround, some
> > > kind of "thing" i can execute on the guest, that would
make the kernel
> > > recheck it''s partition size or something.
> >
> > The problem is not about rereading the partition table; this can be
done
> > using for example "blockdev --rereadpt".
> >
> > The problem is to get the disk device (/dev/xvd*) resized.. ie.
getting the
> > kernel to see the DISK has been resized.
> >
> > After the disk has been resized, partition table can be resized after
that.
> >
> > Disk resizing on the fly is not supported today with Xen.
> 
> Well I understand that it is inside the kernel, but, i''m not using
disks, i''m
> using partitions directly:
> 
> e.g.:
> 
> ''tap:aio:/opt/data/file.img, sda1, w''
> 
> I can make the partition file larger on dom0 no problem, i could even
resize
> the partition live on dom0 no problem.
> 
> But (i guess the kernel) doesn''t see the partition as larger, even
with forced
> operations, i still get read errors at the end.
> 
> I''m not even sure the blktap device detected this change in size
on dom0.
> 
> But if i''m using directly partitions, maybe there is some code
that i can
> execute that does kernel calls or something to refresh it''s
device. ie: a
> workaround.
> 
> I mean, hotplug seems to be able to do it just fine. ie: memory is detected
as
> larger, i imagine there is such code for block devices as well, no? So i 
> figured there should be something i can do in the guest (maybe even on
kernel
> level) that could force the re-detection of the device or something.
> 
> Of course if blktap can''t even pass on the information to the
guest, this
> would not work at all...
> 
Like said, there''s no way for Xen (or dom0) to tell domU that disk or
partition has been resized.
It is not yet implemented.

Solution: Use LVM in domU and xm block-attach new disk/partition to domU, create
PV to
it and add that PV to existing VG.

-- Pasi

_______________________________________________
Xen-users mailing list
Xen-users@lists.xensource.com
http://lists.xensource.com/xen-users

Op Thursday 05 February 2009 16:36:04 schreef Pasi
Kärkkäinen:
> On Thu, Feb 05, 2009 at 03:35:18PM +0100, Maarten Vanraes wrote:
> > Op Thursday 05 February 2009 15:27:55 schreef Pasi Kärkkäinen:
> > > On Thu, Feb 05, 2009 at 01:59:57PM +0100, Maarten Vanraes wrote:
> > > > Op Thursday 05 February 2009 13:05:01 schreef Pasi
Kärkkäinen:
> > > > > On Thu, Feb 05, 2009 at 11:52:56AM +0100, Maarten
Vanraes wrote:
> > > > > > Hi,
> > > > > >
> > > > > > I have 2 questions:
> > > > > >
> > > > > >  1. I was not able to let the guest know that the
partition size
> > > > > > was changed. 2. I was not able to use block-attach
with the same
> > > > > > backendfile to different machines (eg: guest +
dom0)
> > > > > >
> > > > > > I''ve read that block-reconfigure
could''ve been used for this,
> > > > > > except that it wasn''t designed to work
for filebased vbd on PVs,
> > > > > > only for switching CDROMs in HVM
> > > > > >
> > > > > > When you use a local disk on a machine, you can
use fdisk to
> > > > > > change partitions and sizes, it then rereads the
partition table
> > > > > > to reflect those changes.
> > > > > >
> > > > > > Since i''m not using a disk, but directly
partitions, isn''t it
> > > > > > possible to just give a signal to the guest that
it should
> > > > > > recheck the partition? can be from the guest
itself.
> > > > > >
> > > > > > Some kind of workaround?
> > > > >
> > > > > Sorry, this is not possible.
> > > > >
> > > > > There''s a a feature request about it for Xen
3.4.
> > > > >
> > > > > Dunno if it will be implemented.
> > > > >
> > > > > -- Pasi
> > > >
> > > > Yes, i read your thread, i was hoping for some kind of
workaround,
> > > > some kind of "thing" i can execute on the guest,
that would make the
> > > > kernel recheck it''s partition size or something.
> > >
> > > The problem is not about rereading the partition table; this can
be
> > > done using for example "blockdev --rereadpt".
> > >
> > > The problem is to get the disk device (/dev/xvd*) resized.. ie.
getting
> > > the kernel to see the DISK has been resized.
> > >
> > > After the disk has been resized, partition table can be resized
after
> > > that.
> > >
> > > Disk resizing on the fly is not supported today with Xen.
> >
> > Well I understand that it is inside the kernel, but, i''m not
using disks,
> > i''m using partitions directly:
> >
> > e.g.:
> >
> > ''tap:aio:/opt/data/file.img, sda1, w''
> >
> > I can make the partition file larger on dom0 no problem, i could even
> > resize the partition live on dom0 no problem.
> >
> > But (i guess the kernel) doesn''t see the partition as larger,
even with
> > forced operations, i still get read errors at the end.
> >
> > I''m not even sure the blktap device detected this change in
size on dom0.
> >
> > But if i''m using directly partitions, maybe there is some
code that i can
> > execute that does kernel calls or something to refresh it''s
device. ie: a
> > workaround.
> >
> > I mean, hotplug seems to be able to do it just fine. ie: memory is
> > detected as larger, i imagine there is such code for block devices as
> > well, no? So i figured there should be something i can do in the guest
> > (maybe even on kernel level) that could force the re-detection of the
> > device or something.
> >
> > Of course if blktap can''t even pass on the information to the
guest, this
> > would not work at all...
>
> Like said, there''s no way for Xen (or dom0) to tell domU that disk
or
> partition has been resized. It is not yet implemented.
>
> Solution: Use LVM in domU and xm block-attach new disk/partition to domU,
> create PV to it and add that PV to existing VG.
>
> -- Pasi
I don''t follow?

* make new disk file on dom0
* xm block-attach the disk file to domU
* the domU uses LVM based on the disk files
* make on both disks an LVM partition that has the same VolGroup? and 
combining it linearly?

that would mean that adding a PV to the volgroup would make the / bigger? 
enableing myself to use resize2fs on the domU directly?

so if i gather this, it would be the same if i added another device and used 
raid  linear mode as / ?

Sincerely,

Maarten

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Xen-users@lists.xensource.com
http://lists.xensource.com/xen-users

On Thu, Feb 5, 2009 at 10:44 AM, Maarten Vanraes <maarten@ba.be>
wrote:
> that would mean that adding a PV to the volgroup would make the / bigger?
> enableing myself to use resize2fs on the domU directly?
adding a PV (physical volume)  to the VG (volume group) makes the VG
bigger.  then you can grow any LV (logical volume).

IOW, the VG abstracts the PVs.  the LVs don''t care where the storage
is.



-- 
Javier

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Op Thursday 05 February 2009 16:55:44 schreef Javier
Guerra:
> On Thu, Feb 5, 2009 at 10:44 AM, Maarten Vanraes <maarten@ba.be>
wrote:
> > that would mean that adding a PV to the volgroup would make the /
bigger?
> > enableing myself to use resize2fs on the domU directly?
>
> adding a PV (physical volume)  to the VG (volume group) makes the VG
> bigger.  then you can grow any LV (logical volume).
>
> IOW, the VG abstracts the PVs.  the LVs don''t care where the
storage is.
I guess that makes sense...

If i were to choose between this or mdadm with linear mode, which would be 
more efficient? i''m guessing it''d be mdadm. and i
wouldn''t need anything more
than this...

I know LVM is much more flexible though, but i don''t necessarily need
all that
abstraction functionality. I plainly want to enlarge my /.

if i were to use mdadm linear mode, could i migrate to this live? i''m
guessing
not... especially since it''s the /.

1. can i create the linear mode raid without losing data? ie: the first 
partition doesn''t need to be changed, right? I guess this could work.
2. can I switch the / device while it''s being used? i remember that
initrd
have a command that does this (pivot_root) or something...

I guess this is really going off-topic. it would be so much better if the 
propagation would work...

Sincerely,

Maarten

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Op Thursday 05 February 2009 16:55:44 schreef Javier
Guerra:
> On Thu, Feb 5, 2009 at 10:44 AM, Maarten Vanraes <maarten@ba.be>
wrote:
> > that would mean that adding a PV to the volgroup would make the /
bigger?
> > enableing myself to use resize2fs on the domU directly?
>
> adding a PV (physical volume)  to the VG (volume group) makes the VG
> bigger.  then you can grow any LV (logical volume).
>
> IOW, the VG abstracts the PVs.  the LVs don''t care where the
storage is.
Also, if block-reconfigure would work, it would also be nice

1. make a live copy of the partition file but bigger
2. pause the domU
3. mount both in dom0
4. do a last rsync
5. umount again
6. block-reconfigure to the new one
7. unpause the domU 


but i''d prefer growing on dom0 and propagating the change...

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On Thu, Feb 05, 2009 at 04:44:07PM +0100, Maarten Vanraes
wrote:
> Op Thursday 05 February 2009 16:36:04 schreef Pasi Kärkkäinen:
> > On Thu, Feb 05, 2009 at 03:35:18PM +0100, Maarten Vanraes wrote:
> > > Op Thursday 05 February 2009 15:27:55 schreef Pasi Kärkkäinen:
> > > > On Thu, Feb 05, 2009 at 01:59:57PM +0100, Maarten Vanraes
wrote:
> > > > > Op Thursday 05 February 2009 13:05:01 schreef Pasi
Kärkkäinen:
> > > > > > On Thu, Feb 05, 2009 at 11:52:56AM +0100, Maarten
Vanraes wrote:
> > > > > > > Hi,
> > > > > > >
> > > > > > > I have 2 questions:
> > > > > > >
> > > > > > >  1. I was not able to let the guest know that
the partition size
> > > > > > > was changed. 2. I was not able to use
block-attach with the same
> > > > > > > backendfile to different machines (eg: guest
+ dom0)
> > > > > > >
> > > > > > > I''ve read that block-reconfigure
could''ve been used for this,
> > > > > > > except that it wasn''t designed to
work for filebased vbd on PVs,
> > > > > > > only for switching CDROMs in HVM
> > > > > > >
> > > > > > > When you use a local disk on a machine, you
can use fdisk to
> > > > > > > change partitions and sizes, it then rereads
the partition table
> > > > > > > to reflect those changes.
> > > > > > >
> > > > > > > Since i''m not using a disk, but
directly partitions, isn''t it
> > > > > > > possible to just give a signal to the guest
that it should
> > > > > > > recheck the partition? can be from the guest
itself.
> > > > > > >
> > > > > > > Some kind of workaround?
> > > > > >
> > > > > > Sorry, this is not possible.
> > > > > >
> > > > > > There''s a a feature request about it for
Xen 3.4.
> > > > > >
> > > > > > Dunno if it will be implemented.
> > > > > >
> > > > > > -- Pasi
> > > > >
> > > > > Yes, i read your thread, i was hoping for some kind of
workaround,
> > > > > some kind of "thing" i can execute on the
guest, that would make the
> > > > > kernel recheck it''s partition size or
something.
> > > >
> > > > The problem is not about rereading the partition table; this
can be
> > > > done using for example "blockdev --rereadpt".
> > > >
> > > > The problem is to get the disk device (/dev/xvd*) resized..
ie. getting
> > > > the kernel to see the DISK has been resized.
> > > >
> > > > After the disk has been resized, partition table can be
resized after
> > > > that.
> > > >
> > > > Disk resizing on the fly is not supported today with Xen.
> > >
> > > Well I understand that it is inside the kernel, but, i''m
not using disks,
> > > i''m using partitions directly:
> > >
> > > e.g.:
> > >
> > > ''tap:aio:/opt/data/file.img, sda1, w''
> > >
> > > I can make the partition file larger on dom0 no problem, i could
even
> > > resize the partition live on dom0 no problem.
> > >
> > > But (i guess the kernel) doesn''t see the partition as
larger, even with
> > > forced operations, i still get read errors at the end.
> > >
> > > I''m not even sure the blktap device detected this change
in size on dom0.
> > >
> > > But if i''m using directly partitions, maybe there is
some code that i can
> > > execute that does kernel calls or something to refresh
it''s device. ie: a
> > > workaround.
> > >
> > > I mean, hotplug seems to be able to do it just fine. ie: memory
is
> > > detected as larger, i imagine there is such code for block
devices as
> > > well, no? So i figured there should be something i can do in the
guest
> > > (maybe even on kernel level) that could force the re-detection of
the
> > > device or something.
> > >
> > > Of course if blktap can''t even pass on the information
to the guest, this
> > > would not work at all...
> >
> > Like said, there''s no way for Xen (or dom0) to tell domU that
disk or
> > partition has been resized. It is not yet implemented.
> >
> > Solution: Use LVM in domU and xm block-attach new disk/partition to
domU,
> > create PV to it and add that PV to existing VG.
> >
> > -- Pasi
> 
> I don''t follow?
> 
> * make new disk file on dom0
> * xm block-attach the disk file to domU
> * the domU uses LVM based on the disk files
> * make on both disks an LVM partition that has the same VolGroup? and 
> combining it linearly?
> 
You don''t need to have LVM partition on the (extra) disks.. just create
the
PV directly to the device (/dev/xvdb etc).

You have just 1 volgroup, and you add new PV to it, so the volgroup gets
bigger.
> that would mean that adding a PV to the volgroup would make the / bigger? 
> enableing myself to use resize2fs on the domU directly?
>
After the volgroup is bigger, you can extend which ever logical volume you
need to extend.. and after that resize the filesystem.
> so if i gather this, it would be the same if i added another device and
used
> raid linear mode as / ?
> 
Well, however you want to do it :)

-- Pasi

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On Thu, Feb 05, 2009 at 05:12:35PM +0100, Maarten Vanraes
wrote:
> 
> but i''d prefer growing on dom0 and propagating the change...
Of course, that would be the best option. 

Feel free to submit patches.. I''m sure they''ll be gladly
accepted!

-- Pasi

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Op Thursday 05 February 2009 17:37:33 schreef Pasi
Kärkkäinen:
> On Thu, Feb 05, 2009 at 05:12:35PM +0100, Maarten Vanraes wrote:
> > but i''d prefer growing on dom0 and propagating the change...
>
> Of course, that would be the best option.
>
> Feel free to submit patches.. I''m sure they''ll be gladly
accepted!
>
> -- Pasi
I could say the same to you... ;-)

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