How to force GEOM to recalculate the free space after the disk is resized?
Maxim Sobolev
sobomax at freebsd.org
Fri Jul 8 15:20:27 UTC 2016
Smells like a bug in the geom_part where it supposed to re-read the
partitions and update its internal structures. The reason why it works when
you open dev/da1 for writing is because the geom_part provider that is
attached to that disk is destroyed and created anew when you close the fd.
-Maxim
On Fri, Jul 8, 2016 at 5:19 AM, Dexuan Cui <decui at microsoft.com> wrote:
> Hi, I have a FreeBSD virtual machine (VM) running on Hyper-V and I'm
> testing Hyper-V's Disk Online Resizing feature. The feature can expand or
> shrink the (virtual) disk capacity of a VM when the VM is running.
>
> There is an issue with gpart or GEOM: after the disk capacity is expanded
> (or shrunk), gpart/GEOM can detect the new bigger capacity, but the free
> space displayed by gpart remained the same unless I open the disk dev file
> for writing, e.g.,
>
> [root at decui-bsd11 ~]# gpart create -s MBR /dev/da1
> da1 created
> [root at decui-bsd11 ~]# gpart show /dev/da1
> => 63 83886017 da1 MBR (40G)
> 63 83886017 - free - (40G)
> [root at decui-bsd11 ~]# diskinfo /dev/da1
> /dev/da1 512 42949672960 83886080 4096 0
> 5221 255 63
>
> Now I expand the disk from 40GB to 50GB by Hyper-V management tool.
>
> Next, I get the below, i.e., gpart/GEOM detects the new disk capacity, but
> the free space remains the same.
> (Note: the first diskinfo failure should be expected: Hyper-V only
> notifies the VM of the capacity change on the VM's next read or write
> request, and in the VM it seems there is a race condition between the ioctl
> and the handling of capacity change. I'll see how this can be fixed.)
>
> [root at decui-bsd11 ~]# diskinfo /dev/da1
> diskinfo: /dev/da1: ioctl(DIOCGMEDIASIZE) failed, probably not a disk.
> [root at decui-bsd11 ~]# diskinfo /dev/da1
> /dev/da1 512 53687091200 104857600 4096 0
> 6527 255 63
>
> [root at decui-bsd11 ~]# gpart show /dev/da1
> => 63 83886017 da1 MBR (50G)
> 63 83886017 - free - (40G)
>
> Now, if I run a program that only does
> "openat(AT_FDCWD,"/dev/da1",O_WRONLY|O_CREAT,0644);", GEOM will detect that
> the free space is 50GB now and GEOM will pass this info to gpart:
>
> [root at decui-bsd11 ~]# gpart show /dev/da1
> => 63 104857537 da1 MBR (50G)
> 63 104857537 - free - (50G)
>
> I'm not familiar with GEOM.
> Can somebody please explain the behavior?
>
> I don't know who exactly maintains GEOM , so I just picked some names from
> "git log geom/" and put you to Cc. Sorry if this mail bothers you. :-)
>
> Thanks,
> -- Dexuan
>
>
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