Re: LUN resizing

[Stefan Voelkel <Stefan.Voelkel@millenux.com>]

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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
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Stefan Völkel                            stefan.voelkel@millenux.com
Millenux GmbH                              mobile: +49.170.79177.17
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