Storage
The final storage configuration that a deployed node uses can be influenced significantly. MAAS supports traditional disk partitioning as well as more complex options such as LVM, RAID, and Bcache. UEFI is also supported as a boot mechanism.
A node's storage is dependant upon the underlying system's disks but its configuration (how the disks get used) is the result of a storage template. In MAAS this template is called a layout and it gets applied to a node when it is commissioned.
Once a layout is applied, a regular user can make modifications to a node at the filesystem level in order to arrive at the node's final storage configuration.
When a node is no longer needed a user can choose from among several disk erasure types before releasing it.
Note: MAAS supports storage configuration for CentOS and RHEL deployments. Support includes RAID, LVM, and custom partitioning with different file systems (ZFS and Bcache excluded). This support requires a newer version of Curtin, available as a PPA.
UEFI
A node booting with UEFI is supported by every layout type. In such a case, an
EFI boot partition (/boot/efi) will be automatically created. Other than
setting the node to boot from UEFI, no other action is required of the user.
Warning: UEFI is either used by the node throughout its lifecycle or it's not. For example, do not enlist a node with UEFI enabled and then disable it before commissioning. It won't work!
The EFI partition, if created, will be the first partition (sda1) and will
have a FAT32 filesystem with a size of 512 MB.
Layouts
There are three layout types:
- Flat layout
- LVM layout
- Bcache layout
The below layout descriptions will include the EFI partition. If your system is
not using UEFI simply regard sda2 as sda1 (with an additional 512 MB
available to it).
Flat layout
With the Flat layout, a partition spans the entire boot disk. The partition is
formatted with the ext4 filesystem and uses the / mount point:
| Name | Size | Type | Filesystem | Mount point |
|---|---|---|---|---|
| sda | - | disk | ||
| sda1 | 512 MB | part | FAT32 | /boot/efi |
| sda2 | rest of sda | part | ext4 | / |
The following options are supported:
boot_size: Size of the boot partition on the boot disk. Default is 0,
meaning not to create the boot partition. The '/boot' will be placed on
the root filesystem.
root_device: The block device to place the root partition on. Default is the
boot disk.
root_size: Size of the root partition. Default is 100%, meaning the entire
size of the root device.
LVM layout
The LVM layout creates the volume group vgroot on a partition that spans the
entire boot disk. A logical volume lvroot is created for the full size of the
volume group; is formatted with the ext4 filesystem; and uses the / mount point:
| Name | Size | Type | Filesystem | Mount point |
|---|---|---|---|---|
| sda | - | disk | ||
| sda1 | 512 MB | part | FAT32 | /boot/efi |
| sda2 | rest of sda | part | lvm-pv(vgroot) | |
| lvroot | rest of sda | lvm | ext4 | / |
| vgroot | rest of sda | lvm |
The following options are supported:
boot_size: Size of the boot partition on the boot disk. Default is 0, meaning not to
create the boot partition. The '/boot' will be placed on the root filesystem.
root_device: The block device to place the root partition on. Default is the boot disk.
root_size: Size of the root partition. Default is 100%, meaning the entire size of the
root device.
vg_name: Name of the created volume group. Default is vgroot.
lv_name: Name of the created logical volume. Default is lvroot.
lv_size: Size of the created logical volume. Default is 100%, meaning the entire size of
the volume group.
Bcache layout
A Bcache layout will create a partition that spans the entire boot disk as the
backing device. It uses the smallest block device tagged with 'ssd' as the
cache device. The Bcache device is formatted with the ext4 filesystem and uses
the / mount point. If there are no 'ssd' tagged block devices on the node,
then the Bcache device will not be created and the Flat layout will be used
instead:
| Name | Size | Type | Filesystem | Mount point |
|---|---|---|---|---|
| sda | - | disk | ||
| sda1 | 512 MB | part | FAT32 | /boot/efi |
| sda2 | rest of sda | part | bc-backing | |
| sdb (ssd) | - | disk | ||
| sdb1 | 100% of sdb | part | bc-cache | |
| bcache0 | per sda2 | disk | ext4 | / |
The following options are supported:
boot_size: Size of the boot partition on the boot disk. Default is 0, meaning
not to create the boot partition. The '/boot' will be placed on the root
filesystem.
root_device: The block device to place the root partition on. Default is the
boot disk.
root_size: Size of the root partition. Default is 100%, meaning the entire
size of the root device.
cache_device: The block device to use as the cache device. Default is the
smallest block device tagged ssd.
cache_mode: The cache mode to set the created Bcache device to. Default is
writethrough.
cache_size: The size of the partition on the cache device. Default is 100%,
meaning the entire size of the cache device.
cache_no_part: Whether or not to create a partition on the cache device.
Default is false, meaning to create a partition using the given cache_size.
If set to true no partition will be created and the raw cache device will be
used as the cache.
Setting layouts
Layouts can be set globally and on a per-node basis.
Default layout
All nodes will have a default layout applied when commissioned. An administrator can configure the default layout on the 'Settings' page, under the 'Storage' tab.
See Disk erasure for an explanation of the options related to the erasing of disks.
Important: The new default will only apply to newly-commissioned nodes.
To change the default with the CLI see MAAS CLI - advanced tasks.
Node layout
An administrator can change the layout for a single node as well as customise that layout providing this is done while the node has a status of 'Ready'. This is only possible via the CLI at this time (see MAAS CLI - advanced tasks).
Note: Only an administrator can modify storage at the block device level (providing the node has a status of 'Ready').
Final storage modifications
Once a node has been provisioned with block devices via a layout or administrator customisation (as mentioned under 'Node layout'), a regular user can perform modifications on the resulting storage configuration at the filesystem level.
Disk erasure
Node storage can be erased in several ways. See Disk erasure for details.