linux-kernel - Re: [PATCH 0/6] detect online disk resize

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Date:	Fri, 5 Sep 2008 11:21:10 +0300
From:	Pasi Kärkkäinen <pasik@....fi>
To:	Andrew Patterson <andrew.patterson@...com>
Cc:	linux-scsi@...r.kernel.org, James.Bottomley@...senPartnership.com,
	linux-kernel@...r.kernel.org, viro@...iv.linux.org.uk,
	axboe@...nel.dk, andmike@...ux.vnet.ibm.com, mike.miller@...com,
	genanr@...phone.com, jmoyer@...hat.com
Subject: Re: [PATCH 0/6] detect online disk resize

On Thu, Sep 04, 2008 at 02:27:15PM -0600, Andrew Patterson wrote:
> Resubmitting this patch against Jens's linux-2.6-block:for-2.6.28 repo.
> 
> This patch series handles online disk resizes that are currently not
> completely recognized by the kernel using the existing revalidate_disk
> routines.  An online resize can occur when growing or shrinking a
> Fibre Channel LUN or perhaps by adding a disk to an existing RAID
> volume.
> 
> The kernel currently recognizes a device size change when the
> lower-level revalidate_disk routines are called; however, the block
> layer does not use the new size while it has any current openers on
> the device. So, for example, if LVM has an volume open on the device,
> you will generally not see the size change until after a reboot. We
> fix this problem by creating a wrapper to be used with lower-level
> revalidate_disk routines.  This wrapper first calls the lower-level
> driver's revalidate_disk routine. It then compares the gendisk
> capacity to the block devices inode size. If there is a difference, we
> adjust the block device's size. If the size has changed, we then flush
> the disk for safety. The size is also checked in rescan_partitions
> which is called when the device is opened or when the BLKRRPART ioctl
> is called.
> 
> There are several ways to "kick off" a device size change:
> 
> 1. For SCSI devices do:
> 
>   # echo 1 > /sys/class/scsi_device/<device>/device/rescan
> 
>   or
> 
>   # blockdev --rereadpt <device file>
> 
> 2. Other devices (not device mapper)
> 
>   # blockdev --rereadpt <device file>
> 
> I have tested this patch on SCSI and SmartArray (cciss)
> devices. Device mapper still does not recognize device size changes
> until the device is restarted.
> 

Hello and thanks for the patch! 

How about device mapper.. what's needed to make it detect/support online resizes?
I'm specificly interested in online resizing (growing) dm-multipath devices.. 

Basicly I'd like to have LVM PV on dm-multipath device.. so first I need to
get the actual disks resized, then dm-multipath device, and finally run pvresize.

I know dm-multipath part can be done atm using this (hacky) method:
https://www.redhat.com/archives/dm-devel/2008-August/msg00033.html

-- Pasi
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