Does RHEL 7 support online resize of disk partitions?

Resolution

The ability to resize a Logical Volume and filesystem has long been provided by Logical Volume Manager (LVM) by simply using the entire block device (/dev/sdx for example) as a Physical Volume in the LVM Volume Group. There is no need for the old style of partition. This would allow the Logical Volume and filesystem to easily be expanded.

As to older style partitions, this feature has been added in RHEL 7 current release with a feature request (RFE has been filed to add support for online resizing of disk partitions to RHEL 7 in private RHBZ#853105. With this feature, it's possible to resize the disk partitions online in RHEL 7.

Disclaimer: The following information has been provided by Red Hat, but is outside the scope of the posted Service Level Agreements and support procedures (Production Support - Red Hat Customer Portal). The information is provided as-is and any configuration settings or installed applications made from the information in this article could make the Operating System unsupported by Red Hat Global Support Services. The intent of this article is to provide information to accomplish the system's needs. Use of the information in this article at the user's own risk.

From a technical point of view, resizing filesystems and their underlying partitions (making changes to the existing partition table) can be very dangerous. Also, it is only possible to resize partitions from their end position on the disk. It is not possible to move partitions on the disk or resize them from their beginning. Such operations can result in a corrupted partition table, which will render all data on the disk device inaccessible, leading to data loss. While it is possible to perform online partition resize operation, it is not recommended simply from a data integrity standpoint and not because it's not possible.

For additional information check also How can I extend an existing file-system partition without destroying data? article.

• In order to resize online a partition which is in use observe the following steps:

# fdisk -l /dev/vda

Disk /dev/vda: 32.2 GB, 32212254720 bytes, 62914560 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 label type: dos
Disk identifier: 0x000db7e6

   Device Boot      Start         End      Blocks   Id  System
/dev/vda1   *        2048     1026047      512000   83  Linux
/dev/vda2         1026048    28289023    13631488   8e  Linux LVM

# cat /proc/partitions 
major minor  #blocks  name

 252        0   31457280 vda
 252        1     512000 vda1
 252        2   13631488 vda2
  11        0    1048575 sr0
 253        0   10240000 dm-0
 253        1    2129920 dm-1

# pvs
  PV         VG          Fmt  Attr PSize  PFree
  /dev/vda2  rhel_vm-205 lvm2 a--  13.00g 1.20g

• Modify the on-disk partition table as usual (e.g. by using fdisk command).

  • Delete the partition:

    Command (m for help): d
    Partition number (1,2, default 2): 2
    Partition 2 is deleted
    

  • Re-create the partition with the new size:

    Command (m for help): n
    Partition type:
       p   primary (1 primary, 0 extended, 3 free)
       e   extended
    Select (default p): p
    Partition number (2-4, default 2): 2
    First sector (1026048-62914559, default 1026048): 
    Using default value 1026048
    Last sector, +sectors or +size{K,M,G} (1026048-62914559, default 62914559): +18G
    Partition 2 of type Linux and of size 18 GiB is set
    
    Command (m for help): t
    Partition number (1,2, default 2): 2
    Hex code (type L to list all codes): 8e
    Changed type of partition 'Linux' to 'Linux LVM'
    
    Command (m for help): p
    
    Disk /dev/vda: 32.2 GB, 32212254720 bytes, 62914560 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 label type: dos
    Disk identifier: 0x000db7e6
    
       Device Boot      Start         End      Blocks   Id  System
    /dev/vda1   *        2048     1026047      512000   83  Linux
    /dev/vda2         1026048    38774783    18874368   8e  Linux LVM
    

  • Commit changes to on-disk partition table:

    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.
    

  • While on-disk partition table has been updated, observe that on-memory kernel partition table has not:

    # partprobe 
    Error: Partition(s) 2 on /dev/vda have been written, but we have been unable to inform the kernel of the change, probably because it/they are in use.  As a result, the old partition(s) will remain in use.  You should reboot now before making further changes.
    
    # cat /proc/partitions | grep vd
     252        0   31457280 vda
     252        1     512000 vda1
     252        2   13631488 vda2
    

• Execute partx (provided by util-linux package) with --update option on the block device to update the in-memory kernel partition table from the on-disk partition table:

  # partx -u /dev/vda
  

• Verify that in-memory kernel partition table has been updated with the new size:

  # cat /proc/partitions | grep vd
   252        0   31457280 vda
   252        1     512000 vda1
   252        2   18874368 vda2
  

• Proceed with any further steps, in this example by extending the PV on the partition:

  # pvresize /dev/vda2
    Physical volume "/dev/vda2" changed
    1 physical volume(s) resized / 0 physical volume(s) not resized
  
  # pvs
    PV         VG          Fmt  Attr PSize  PFree
    /dev/vda2  rhel_vm-205 lvm2 a--  18.00g 6.20g