LUN resizing

LUN resizing

[Stefan Voelkel]

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Hello,

a hypothetical question:

I have a Linux box connected to a Fibre SAN. Now I'd like to resize one
LUN and tell my Linux box what happened. In other words can I _live_
resize a SCSI disk?

        [ let's not talk about which filesystems are capable of live
        resizing :) ]
        
      * Is this possible at all, eg does the SCSI Standard include
        something to enable a device to tell the host about the changed
        geometry (SENSE DATA, ...) ?
      * Is it possible with Linux, eg does the block layer/scsi layer
        support it? any problems with the partition code?
      * If there are problems, are they solveable, any plans on working
        on them or is already someone working on this?

Two options come to my mind:
      * LVM, just define a new LUN, add it to the group, and resize
      * echo remove-single-device ... > /proc/scsi/scsi (would not be
        life)


regards
	Stefan
-- 
--------------------------------------------------------------------
Stefan Völkel                            stefan.voelkel@millenux.com
Millenux GmbH                              mobile: +49.170.79177.17
Lilienthalstraße 2                          phone: +49.711.88770.300
70825 Stuttgart-Korntal                       fax: +49.711.88770.349
     -= linux without limits -=- http://linux.zSeries.org/ =-

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Re: LUN resizing

[James Bottomley]

On Tue, 2003-11-25 at 03:34, Stefan Voelkel wrote:
> I have a Linux box connected to a Fibre SAN. Now I'd like to resize one
> LUN and tell my Linux box what happened. In other words can I _live_
> resize a SCSI disk?
> 
>         [ let's not talk about which filesystems are capable of live
>         resizing :) ]
>         
>       * Is this possible at all, eg does the SCSI Standard include
>         something to enable a device to tell the host about the changed
>         geometry (SENSE DATA, ...) ?

The pull command is READ_CAPACITY.  For pushing this information,
there's nothing really standard, although some type of proprietary AEN
could be adapted.

>       * Is it possible with Linux, eg does the block layer/scsi layer
>         support it? any problems with the partition code?
>       * If there are problems, are they solveable, any plans on working
>         on them or is already someone working on this?

You simply do

echo 1 > /sys/bus/scsi/<device>/rescan

It will re-read the capacity and partition table (as long as the device
is unmounted and none of the partitions open).

James

Re: LUN resizing

[James Bottomley]

On Tue, 2003-11-25 at 09:43, James Bottomley wrote:
> You simply do
> 
> echo 1 > /sys/bus/scsi/<device>/rescan
> 
> It will re-read the capacity and partition table (as long as the device
> is unmounted and none of the partitions open).

OK, I actually tried this, you need two steps.  The one above will
reread the capacity.  After that you send a BLKRRPART ioctl to the
device to re-read the partition table. (but, obviously, something else
will have to update the partition table to see the new device size)

James

Re: LUN resizing

[Stefan Voelkel]

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On Tue, 2003-11-25 at 17:11, James Bottomley wrote:
> On Tue, 2003-11-25 at 09:43, James Bottomley wrote:
> > You simply do
> > 
> > echo 1 > /sys/bus/scsi/<device>/rescan
> > 
> > It will re-read the capacity and partition table (as long as the device
> > is unmounted and none of the partitions open).
>
> OK, I actually tried this, you need two steps.  The one above will
> reread the capacity.  After that you send a BLKRRPART ioctl to the
> device to re-read the partition table. (but, obviously, something else
> will have to update the partition table to see the new device size)

Ok, that is a step in the right direction, as it will not disrupt
operations of other devices on the same bus.

But I want to be able to do it with a mounted partition, something like
"device size hotpluging". I don't know if that is the right term, but
think of the 2.7 memory hotplug plans.

      * in the SAN I add space to my LUN
      * then I hit my linux box on the head to get it to send a
        read_capacity and update the size of the device.
      * run a nifty tool that creates a new partition table and writes
        it to the device.
      * use newly gained space

so what we actually need is:

      * a way to force the scsi stack to send out a read_capacity and
        act on it (perhaps another /sys/ entry?), perhaps a hotplug
        event that creates a new partition table, eg add the new space
        as "unused" at the end of the device, write that table and
        ioctl() to reread it.
      * a way to fiddle around with live partitions,  a userspace tool
        with a way to tell the kernel supsend/reactivate io on that
        block device. it would have to take care of the filesystems
        residing on the device.

regards
	Stefan
-- 
--------------------------------------------------------------------
Stefan Völkel                            stefan.voelkel@millenux.com
Millenux GmbH                              mobile: +49.170.79177.17
Lilienthalstraße 2                          phone: +49.711.88770.300
70825 Stuttgart-Korntal                       fax: +49.711.88770.349
     -= linux without limits -=- http://linux.zSeries.org/ =-

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Re: LUN resizing

[Christoph Hellwig]

On Wed, Nov 26, 2003 at 10:45:11AM +0100, Stefan Voelkel wrote:
>       * a way to force the scsi stack to send out a read_capacity and
>         act on it (perhaps another /sys/ entry?), perhaps a hotplug
>         event that creates a new partition table, eg add the new space
>         as "unused" at the end of the device, write that table and
>         ioctl() to reread it.
>       * a way to fiddle around with live partitions,  a userspace tool
>         with a way to tell the kernel supsend/reactivate io on that
>         block device. it would have to take care of the filesystems
>         residing on the device.

No way.  You're better of using a proper volume manager instead of doing
this paritioning mess.

Re: LUN resizing

[Stefan Voelkel]

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On Wed, 2003-11-26 at 10:48, Christoph Hellwig wrote:
> On Wed, Nov 26, 2003 at 10:45:11AM +0100, Stefan Voelkel wrote:
> >       * a way to force the scsi stack to send out a read_capacity and
> >         act on it (perhaps another /sys/ entry?), perhaps a hotplug
> >         event that creates a new partition table, eg add the new space
> >         as "unused" at the end of the device, write that table and
> >         ioctl() to reread it.
> >       * a way to fiddle around with live partitions,  a userspace tool
> >         with a way to tell the kernel supsend/reactivate io on that
> >         block device. it would have to take care of the filesystems
> >         residing on the device.
> 
> No way.  You're better of using a proper volume manager instead of doing
> this paritioning mess.

True, let's forget about the partitions: mount /dev/sda /home. 
-- 
--------------------------------------------------------------------
Stefan Völkel                            stefan.voelkel@millenux.com
Millenux GmbH                              mobile: +49.170.79177.17
Lilienthalstraße 2                          phone: +49.711.88770.300
70825 Stuttgart-Korntal                       fax: +49.711.88770.349
     -= linux without limits -=- http://linux.zSeries.org/ =-

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Re: LUN resizing

[Christoph Hellwig]

On Fri, Nov 28, 2003 at 11:08:49AM +0100, Stefan Voelkel wrote:
> > No way.  You're better of using a proper volume manager instead of doing
> > this paritioning mess.
> 
> True, let's forget about the partitions: mount /dev/sda /home. 

Indeed.  If you're resizing luns they're most likely virtualized
alreday anyway :)

Re: LUN resizing

[James Bottomley]

On Fri, 2003-11-28 at 04:08, Stefan Voelkel wrote:
> True, let's forget about the partitions: mount /dev/sda /home. 

OK, Let's try again in simpler terms.

The problem you are trying to solve has three components:

1. Filesystem resize
2. parition resize
3. SCSI device resize

1 and 3 are solved (for a subset of fs).  A solution to 2 is to use the
Linux device mapper (a mini volume manager) to replace the use of
gendisk partitions.  Then your entire stack constructed this way will be
resizable.

The place to begin finding out about DM is the development lists:

dm-devel@sistina.com

With a list archive at:

http://lists.sistina.com/pipermail/dm-devel/

James

Re: LUN resizing

[Lincoln Dale]

At 02:43 AM 26/11/2003, James Bottomley wrote:
>You simply do
>
>echo 1 > /sys/bus/scsi/<device>/rescan
>
>It will re-read the capacity and partition table (as long as the device
>is unmounted and none of the partitions open).

i guess that kinda defeats the purpose of online resizing; the idea is that 
the partitions DO remain mounted and the partitions with a refcount against 
them!


cheers,

lincoln.

Re: LUN resizing

[christophe varoqui]

> The problem you are trying to solve has three components:
> 
> 1. Filesystem resize
> 2. parition resize
> 3. SCSI device resize
> 
> 1 and 3 are solved (for a subset of fs).  A solution to 2 is to use the
> Linux device mapper (a mini volume manager) to replace the use of
> gendisk partitions.  Then your entire stack constructed this way will be
> resizable.

Yes, this idea is floating around :
See the dmpartx post covered at http://lwn.net/Articles/13958/

May be someone (Andries B) will get something like that in initramfs for
2.7 ...

regards,
cvaroqui