MAAS storage reference

This page describes standard and custom storage layouts available in MAAS.

Standard storage layouts

The layout descriptions below will include the EFI partition. If your system is not using UEFI, 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 three options are supported:

  1. 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.

  2. root_device: The block device on which to place the root partition. The default is the boot disk.

  3. 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 six options are supported:

  1. 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.
  2. root_device: The block device on which to place the root partition. The default is the boot disk.
  3. root_size: Size of the root partition. Default is 100%, meaning the entire size of the root device.
  4. vg_name: Name of the created volume group. Default is vgroot.
  5. lv_name: Name of the created logical volume. Default is lvroot.
  6. 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 machine, 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 seven options are supported:

  1. 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.
  2. root_device: The block device upon which to place the root partition. The default is the boot disk.
  3. root_size: Size of the root partition. Default is 100%, meaning the entire size of the root device.
  4. cache_device: The block device to use as the cache device. Default is the smallest block device tagged ssd.
  5. cache_mode: The cache mode to which MAAS should set the created bcache device. The default is writethrough.
  6. cache_size: The size of the partition on the cache device. Default is 100%, meaning the entire size of the cache device.
  7. 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.

vmfs6 storage layout reference

VMFS6 layout

The VMFS6 layout is used for VMware ESXi deployments only. It is required when configuring VMware VMFS Datastores. This layout creates all operating system partitions, in addition to the default datastore. The datastore may be modified. New datastores may be created or extended to include other storage devices. The base operating system partitions may not be modified because VMware ESXi requires them. Once applied another storage layout must be applied to remove the operating system partitions.

Name Size Type Use
sda - disk
sda1 3 MB part EFI
sda2 4 GB part Basic Data
sda3 Remaining part VMFS Datastore 1
sda4 - skipped
sda5 249 MB part Basic Data
sda6 249 MB part Basic Data
sda7 109 MB part VMware Diagnostic
sda8 285 MB part Basic Data
sda9 2.5 GB part VMware Diagnostic

The following options are supported:

  • root_device: The block device upon which to place the root partition. Default is the boot disk.

  • root_size: Size of the default VMFS Datastore. Default is 100%, meaning the remaining size of the root disk.

Blank layout

The blank layout removes all storage configuration from all storage devices. It is useful when needing to apply a custom storage configuration.

Machines with the blank layout applied are not deployable; you must first configure storage manually.

Custom storage layouts

This section explains how to configure custom storage layouts for MAAS-deployed machines. Note that custom storage is only available for MAAS versions 3.1 and higher.

MAAS version 3.1 and higher allow you to define a custom storage layout for a machine, via a custom commissioning script. You must upload a script which conforms to the following rules:

  • it must run after the 40-maas-01-machine-resources script and before the 50-maas-01-commissioning one, so it should have a name that starts with anything between 41- and 49-. This ensures the script can access the JSON file created by the former which provides info about the machine hardware and network resources. In addition, the custom script can directly inspect the machine it’s running on to determine how to configure storage.
  • it can read machine hardware/network information from the JSON file at the path specified by $MAAS_RESOURCES_FILE
  • it must output a JSON file at the path specified by $MAAS_STORAGE_CONFIG_FILE with the desired storage layout
  • names of disks provided in the custom layout must match the ones detected by MAAS and provided in the resources file.

Config format

The configuration contains two main sections:

  • layout, which lists the desired storage layout in terms of disks and volumes, along with their setup (partitions, volumes, …).
    This consists of a dictionary of device names and their configuration. Each device must have a type property (see below for supported types).
  • mounts, which lists the desired filesystem mount points.
    As an example:
"mounts": {
  "/": {
    "device": "sda2",
    "options": "noatime"
  },
  "/boot/efi": {
    "device": "sda1"
  },
  "/data": {
    "device": "raid0"
  }     
}

A complete $MAAS_STORAGE_CONFIG_FILE would look like this:

{
    "layouts": {
        "sda": {
           ...
        },
        "raid0": {
           ...
        },
        ...
    },
    "mounts": {
       "/": {
           ...
       },
       ...
    }
}

The following device types are supported in the "layout" section:

Disk

"sda": {
  "type": "disk",
  "ptable": "gpt",
  "boot": true,
  "partitions": [
    {
      "name": "sda1",
      "fs": "vfat",
      "size": "100M"
      "bootable": true,
    }
  ]
}

A disk entry defines a physical disk.
The following details can be specified:

  • the partition table type (ptable), which can be gpt or mbr
  • whether it should be selected as boot disk
  • optionally, a list of partitions to create, with their size and filesystem type (fs)

LVM

"lvm0": {
  "type": "lvm",
  "members": [
    "sda1",
    "sdb1",
  ],
  "volumes": [
    {
      "name": "data1",
      "size": "5G",
      "fs": "ext4"
    },
    {
      "name": "data2",
      "size": "7G",
      "fs": "btrfs"
    }
  ]
}

An lvm entry defines a VG (volume group) composed by a set of disks or partitions (listed as members). Optionally it’s possible to specify the the LVs (logical volumes) to create.
Those are defined similarly to partitions, with a name and size (and optionally the filesystem).

Bcache

"bcache0": {
  "type": "bcache",
  "cache-device": "sda",
  "backing-device": "sdf3",
  "cache-mode": "writeback",
  "fs": "ext4"
}

A bcache entry must specify a device to use as cache and one to use as storage. Both can be either a partition or a disk.
Optionally the cache-mode for the Bcache can be specified.

RAID

"myraid": {
  "type": "raid",
  "level": 5,
  "members": [
    "sda",
    "sdb",
    "sdc",
  ],
  "spares": [
    "sdd",
    "sde"
  ],
  "fs": "btrfs"

A raid entry defines a RAID with a set of member devices.
Spare devices can also be specified.

Config examples

Here’s a few examples of custom storage layout configurations that a script could output to the $MAAS_STORAGE_CONFIG_FILE. The examples assumes that the machine has 5 disks (named sda to sde).

Note that there’s no need to add entries for those devices in the layout section if the disks are not explicitly partitioned, but just used by other devices (e.g. RAID or LVM).

Simple single-disk layout with GPT partitioning

{
  "layout": {
    "sda": {
      "type": "disk",
      "ptable": "gpt",
      "boot": true,
      "partitions": [
        {
          "name": "sda1",
          "fs": "vfat",
          "size": "500M",
          "bootable": true
        },
        {
          "name": "sda2",
          "size": "5G",
          "fs": "ext4"
        },
        {
          "name": "sda3",
          "size": "2G",
          "fs": "swap"
        },
        {
          "name": "sda4",
          "size": "120G",
          "fS": "ext4"
        }
      ]
    }
  },
  "mounts": {
    "/": {
      "device": "sda2",
      "options": "noatime"
    },
    "/boot/efi": {
      "device": "sda1"
    },
    "/data": {
      "device": "sda4"
    },
    "none": {
      "device": "sda3"
    }
  }
}

In the mounts section, options for mount points can be specified. For swap, an entry must be present (with any unique name that doesn’t start with a /), otherwise the swap will be created but not activated.

RAID 5 setup (with spare devices)

{
  "layout": {
    "storage": {
      "type": "raid",
      "level": 5,
      "members": [
        "sda",
        "sdb",
        "sdc"
      ],
      "spares": [
        "sdd",
        "sde"
      ],
      "fs": "btrfs"
    }
  },
  "mounts": {
    "/data": {
      "device": "storage"
    }
  }
}

Both full disks and partitions can be used as RAID members.

LVM with pre-defined volumes

{
  "layout": {
    "storage": {
      "type": "lvm",
      "members": [
        "sda",
        "sdb",
        "sdc",
        "sdd"
      ],
      "volumes": [
        {
          "name": "data1",
          "size": "1T",
          "fs": "ext4"
        },
        {
          "name": "data2",
          "size": "2.5T",
          "fs": "btrfs"
        }
      ]
    }
  },
  "mounts": {
    "/data1": {
      "device": "data1"
    },
    "/data2": {
      "device": "data2"
    }
  }
}

If no volumes are specified, the volume group is still created.

Bcache

{
  "layout": {
     "data1": {
      "type": "bcache",
      "cache-device": "sda",
      "backing-device": "sdb",
      "cache-mode": "writeback",
      "fs": "ext4"
    },
    "data2": {
      "type": "bcache",
      "cache-device": "sda",
      "backing-device": "sdc",
      "fs": "btrfs"
    }
  },
  "mounts": {
    "/data1": {
      "device": "data1"
    },
    "/data2": {
      "device": "data2"
    }
  }
}

The same cache set can be used by different bcaches by specifying the same backing-device for them.

LVM on top of RAID with Bcache

{
  "layout": {
    "bcache0": {
      "type": "bcache",
      "backing-device": "sda",
      "cache-device": "sdf"
    },
    "bcache1": {
      "type": "bcache",
      "backing-device": "sdb",
      "cache-device": "sdf"
    },
    "bcache2": {
      "type": "bcache",
      "backing-device": "sdc",
      "cache-device": "sdf"
    },
    "bcache3": {
      "type": "bcache",
      "backing-device": "sdd",
      "cache-device": "sdf"
    },
    "bcache4": {
      "type": "bcache",
      "backing-device": "sde",
      "cache-device": "sdf"
    },
    "raid": {
      "type": "raid",
      "level": 5,
      "members": [
        "bcache0",
        "bcache1",
        "bcache2"
      ],
      "spares": [
        "bcache3",
        "bcache4"
      ]
    },
    "lvm": {
      "type": "lvm",
      "members": [
        "raid"
      ],
      "volumes": [
        {
          "name": "root",
          "size": "10G",
          "fs": "ext4"
        },
        {
          "name": "data",
          "size": "3T",
          "fs": "btrfs"
        }
      ]
    }
  },
  "mounts": {
   "/": {
      "device": "root"
    },
    "/data": {
      "device": "data"
    }
  }
}

The RAID is created by using 5 bcache devices, each one using a different disk and the same SSD cache device. LVM is created on top of the RAID device and volumes are then created in it, to provide partitions.

Last updated a month ago.

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