scmanjarrez · May 17, 2022 09:57 · Oct 22, 2012 · Oct 22, 2012
diff --git a/gistfile1.md b/gistfile1.md
@@ -7,6 +7,13 @@ This process assumes the following:
   and I will describe that in another post.
 - The partition you need to resize is the last partition on the disk.
 
+This process will work with either a `qcow2` or `raw` disk image.  For
+`raw` images you can also run `fdisk` on the host, potentially saving
+yourself a reboot, but that's less convenient for `qcow2` format
+images.
+
+---
+
 We start with a 5.5G root filesystem with 4.4G free:
 
     [root@localhost ~]# df -h /

diff --git a/gistfile1.md b/gistfile1.md
@@ -0,0 +1,152 @@
+Occasionally we will deploy a virtual instance into our KVM
+infrastructure and realize after the fact that we need more local disk
+space available.  This is the process we use to expand the disk image.
+This process assumes the following:
+
+- You're using legacy disk partitions.  The process for LVM is similar
+  and I will describe that in another post.
+- The partition you need to resize is the last partition on the disk.
+
+We start with a 5.5G root filesystem with 4.4G free:
+
+    [root@localhost ~]# df -h /
+    Filesystem      Size  Used Avail Use% Mounted on
+    /dev/vda2       5.5G  864M  4.4G  17% /
+
+We need to shut down the system to grow the underlying image:
+
+    [root@localhost ~]# poweroff
+
+On the host, we use the `qemu-img resize` command to grow the image.
+First we need the path to the underlying disk image:
+
+    [lars@madhatter blog]$ virsh -c qemu:///system dumpxml lars-test-0 | grep file
+        <disk type='file' device='disk'>
+          <source file='/var/lib/libvirt/images/lars-test-0-1.img'/>
+
+And now we increase the image size by 10G:
+
+    [lars@madhatter blog]$ sudo qemu-img resize /var/lib/libvirt/images/lars-test-0.img +10G
+    Image resized.
+
+Now reboot the instance:
+
+    [lars@madhatter blog]$ virsh -c qemu:///system start lars-test-0
+
+And login in on the console:
+
+    [lars@madhatter blog]$ virsh -c qemu:///system console lars-test-0
+    Connected to domain lars-test-0
+    Escape character is ^]
+
+    Fedora release 17 (Beefy Miracle)
+    Kernel 3.6.2-4.fc17.x86_64 on an x86_64 (ttyS0)
+
+    localhost login: root
+    Password:
+
+We're going to use `fdisk` to modify the partition layout.  Run
+`fdisk` on the system disk:
+
+    [root@localhost ~]# fdisk /dev/vda
+    Welcome to fdisk (util-linux 2.21.2).
+
+    Changes will remain in memory only, until you decide to write them.
+    Be careful before using the write command.
+
+Print out the existing partition table and verify that you really are
+going to be modifying the final partition:
+
+    Command (m for help): p
+
+    Disk /dev/vda: 19.3 GB, 19327352832 bytes
+    16 heads, 63 sectors/track, 37449 cylinders, total 37748736 sectors
+    Units = sectors of 1 * 512 = 512 bytes
+    Sector size (logical/physical): 512 bytes / 512 bytes
+    I/O size (minimum/optimal): 512 bytes / 512 bytes
+    Disk identifier: 0x00007d9f
+
+       Device Boot      Start         End      Blocks   Id  System
+    /dev/vda1   *        2048     1026047      512000   83  Linux
+    /dev/vda2         1026048     5154815     2064384   82  Linux swap / Solaris
+    /dev/vda3         5154816    16777215     5811200   83  Linux
+
+Delete and recreate the final partition, in this case `/dev/vda3`...
+
+    Command (m for help): d
+    Partition number (1-4): 3
+    Partition 3 is deleted
+
+...and create a new partition, accepting all the defaults.  This will
+create a new partition starting int he same place and extending to the
+end of the disk:
+
+    Command (m for help): n
+    Partition type:
+       p   primary (2 primary, 0 extended, 2 free)
+       e   extended
+    Select (default p): p
+    Partition number (1-4, default 3): 3
+    First sector (5154816-37748735, default 5154816): 
+    Using default value 5154816
+    Last sector, +sectors or +size{K,M,G} (5154816-37748735, default 37748735): 
+    Using default value 37748735
+    Partition 3 of type Linux and of size 15.6 GiB is set
+
+You can print out the new partition table to see that indeed
+`/dev/vda3` is now larger:
+
+    Command (m for help): p
+
+    Disk /dev/vda: 19.3 GB, 19327352832 bytes
+    16 heads, 63 sectors/track, 37449 cylinders, total 37748736 sectors
+    Units = sectors of 1 * 512 = 512 bytes
+    Sector size (logical/physical): 512 bytes / 512 bytes
+    I/O size (minimum/optimal): 512 bytes / 512 bytes
+    Disk identifier: 0x00007d9f
+
+       Device Boot      Start         End      Blocks   Id  System
+    /dev/vda1   *        2048     1026047      512000   83  Linux
+    /dev/vda2         1026048     5154815     2064384   82  Linux swap / Solaris
+    /dev/vda3         5154816    37748735    16296960   83  Linux
+
+Write the changes to disk:
+
+    Command (m for help): w
+    The partition table has been altered!
+
+    Calling ioctl() to re-read partition table.
+
+    WARNING: Re-reading the partition table failed with error 16: Device or resource busy.
+    The kernel still uses the old table. The new table will be used at
+    the next reboot or after you run partprobe(8) or kpartx(8)
+    Syncing disks.
+
+**Note the warning!**  The kernel has cached a copy of the old
+partition table.  We need to reboot the system before our changes are
+visible!  So we reboot the system:
+
+    [root@localhost ~]# reboot
+
+And log back in.  Run `df` to see the current size of the root
+filesystem:
+
+    [root@localhost ~]# df -h /
+    Filesystem      Size  Used Avail Use% Mounted on
+    /dev/vda3       5.5G  864M  4.4G  17% /
+
+Now run `resize2fs` to resize the root filesystem so that it expands
+to fill our extended `/dev/vda3`:
+
+    [root@localhost ~]# resize2fs /dev/vda3
+    resize2fs 1.42.3 (14-May-2012)
+    Filesystem at /dev/vda3 is mounted on /; on-line resizing required
+    old_desc_blocks = 1, new_desc_blocks = 1
+    The filesystem on /dev/vda3 is now 4074240 blocks long.
+
+Run `df` again to see that we now have additional space available:
+
+    [root@localhost ~]# df -h /
+    Filesystem      Size  Used Avail Use% Mounted on
+    /dev/vda3        16G  867M   14G   6% /
+    [root@localhost ~]#