On Wed, May 31, 2017 at 2:51 PM, Gianluca Cecchi <gianluca.cecchi@gmail.com> wrote:

Hello,
I seem to remember that online resize of VirtIO disk is possible.
Now I have an Oracle Linux VM with 2.6.39-400.215.3.el6uek.x86_64 kernel where I resize a disk (/dev/vdb) from 500Gb to 900Gb.
Apparently the kernel acquired the change because in /var/log/messages I see:

May 31 14:16:16 dbatest3 kernel: virtio_blk virtio6: new size: 1887436800 512-byte logical blocks (966 GB/900 GiB)

but fdisk seems not to be able to recognize it:

[root@dbatest3 ~]# fdisk -l /dev/vdb

Disk /dev/vdb: 536.9 GB, 536870912000 bytes
16 heads, 63 sectors/track, 1040253 cylinders
Units = cylinders of 1008 * 512 = 516096 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000

[root@dbatest3 ~]#

It seems that one of these two commands got the change available:

[root@dbatest3 ~]# blockdev --flushbufs /dev/vdb

[root@dbatest3 ~]# blockdev --rereadpt /dev/vdb

Now

[root@dbatest3 ~]# fdisk -l /dev/vdb

Disk /dev/vdb: 966.4 GB, 966367641600 bytes

16 heads, 63 sectors/track, 1872457 cylinders

Units = cylinders of 1008 * 512 = 516096 bytes

Sector size (logical/physical): 512 bytes / 512 bytes

I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk identifier: 0x00000000

[root@dbatest3 ~]# tail -3 /var/log/messages

May 31 14:16:16 dbatest3 kernel: virtio_blk virtio6: new size: 1887436800 512-byte logical blocks (966 GB/900 GiB)

May 31 15:13:49 dbatest3 kernel: vdb: detected capacity change from 536870912000 to 966367641600

May 31 15:13:49 dbatest3 kernel: vdb: unknown partition table

[root@dbatest3 ~]#

I found the hint/suggestion through this proxmox thread:

http://pve-devel.pve.proxmox.narkive.com/LBZ1yFpv/online-resize-of-virtio-blk

Just in case other guys need the same... ;-)