> ## Documentation Index > Fetch the complete documentation index at: https://docs.siderolabs.com/llms.txt > Use this file to discover all available pages before exploring further. # Select the Install Disk > Select the disk Omni installs Talos on, by its path or by a disk selector. A machine that boots Talos from an ISO or over PXE runs it in memory until Talos is installed to a disk. Omni installs Talos when the machine is added to a cluster, or when you select **Install Talos** for it on the **Machines** page. A machine booted from a disk image is already installed, so the install disk does not apply to it. Installing Talos is a one-time operation. On an installed machine, Omni always uses the disk Talos is installed on. A different install disk is used only after the machine is wiped and Talos is installed again. Omni selects the install disk automatically. To use a different disk, select it for the machine. The selection is stored in the `MachineInstallDiskConfig` resource, which has the machine ID as its ID. It belongs to the machine, not to a cluster, so it is kept when the machine is removed from a cluster. > [!NOTE] > > The `MachineInstallDiskConfig` resource and disk selectors require Omni v1.11.0 or later. > > Config patches cannot set the install disk. > Omni rejects patches that set `machine.install.disk` and patches that contain an `UnattendedInstallConfig` document. ## Select the install disk You can select the disk by its path, e.g., `/dev/sdb`, or by a [disk selector](#disk-selectors). A disk path or a disk selector can select any disk of the machine, including the disks the automatic selection skips. Make sure it does not match a member of an MD RAID array, since installing Talos to it breaks the array. > [tab] UI > > On the cluster create and scale pages, assign the machine to the control plane or to a worker machine set. > An **Install Disk** dropdown then appears next to it, unless the machine is already installed: > > * **Auto**: no selection, Omni selects the disk automatically. > The disk it currently selects is shown next to it in parentheses. > * A disk path, e.g., **/dev/sdb**: selects that disk. > Disks built on top of other disks show their member disks, e.g., **/dev/md0 (on sdb, sdc)**. > * **Selector**: shown when the machine has a disk selector. > The disk the selector currently matches is shown next to it in parentheses. > Hover over it to see the expression. > > The dropdown lists only the disks marked `selectable` in [`MachineInstallDiskStatus`](#check-the-install-disk-of-a-machine). > The UI cannot create disk selectors. > Use cluster templates, `omnictl` or Terraform for them. > > The **Install Talos** action on the **Machines** page has its own **Install Disk** dropdown. > It defaults to the disk Omni selects for the machine. > The disk you pick there is used only for that install, and it is not stored in `MachineInstallDiskConfig`. > [tab] Cluster templates > > Set `install.disk` or `install.diskSelector` in the `Machine` document. > They are mutually exclusive. > > ```yaml theme={null} > kind: Machine > name: 27c16241-96bf-4f17-9579-ea3a6c4a3ca8 > install: > diskSelector: disk.serial == "S3EVNX0K123456" > ``` > > * Removing the `install` section deletes the `MachineInstallDiskConfig` created by the template, so Omni selects the disk automatically again. > A `MachineInstallDiskConfig` created in the UI, with `omnictl` or with Terraform is kept. > * Removing the machine from the template keeps its `MachineInstallDiskConfig`. > > See the [cluster templates reference](https://docs.siderolabs.com/omni/reference/cluster-templates.md#machine) for the other fields of the `Machine` document. > [tab] CLI > > 1. Create a `MachineInstallDiskConfig` file named `install-disk.yaml`, using the machine ID as the resource ID: > > ```yaml theme={null} > metadata: > namespace: default > type: MachineInstallDiskConfigs.omni.sidero.dev > id: > spec: > diskselector: disk.serial == "S3EVNX0K123456" > ``` > > To select the disk by its path, set `disk: /dev/sdb` instead of `diskselector`. > > 2. Apply it: > > ```bash theme={null} > omnictl apply -f install-disk.yaml > ``` > > To let Omni select the disk automatically again, delete the resource: > > ```bash theme={null} > omnictl delete machineinstalldiskconfigs > ``` > [tab] Terraform > > Use the [`omni_machine_install_disk`](https://registry.terraform.io/providers/siderolabs/omni/latest/docs/resources/machine_install_disk) resource: > > ```hcl theme={null} > resource "omni_machine_install_disk" "this" { > machine_id = "27c16241-96bf-4f17-9579-ea3a6c4a3ca8" > disk_selector = "disk.serial == \"S3EVNX0K123456\"" > } > ``` > > To select the disk by its path, set `disk = "/dev/sdb"` instead of `disk_selector`. ## Automatic selection When a machine has no `MachineInstallDiskConfig`, Omni selects the smallest disk that is: * larger than 5 GB * not read-only and not a CD-ROM drive * not a member of another disk, e.g., a disk in an MD RAID array * not built on top of other disks, e.g., an MD RAID array or a device-mapper volume USB disks are selected only when no other disk qualifies. From disks of the same size, Omni selects the first one by path. ## Disk selectors A disk selector is a Common Expression Language (CEL) expression evaluated against every disk of the machine. It uses the same variables as the [Talos disk selectors](https://docs.siderolabs.com/talos/v1.14/configure-your-talos-cluster/storage-and-disk-management/disk-management/common.md#disk-selector). A disk selector can target disks by their stable properties: * `disk.serial == "S3EVNX0K123456"`: the disk with this serial number. * `'/dev/disk/by-path/pci-0000:00:1f.2-ata-1' in disk.symlinks`: the disk with this stable symlink. * `'/dev/disk/by-id/md-name-talos:boot' in disk.symlinks`: the MD RAID array named `boot`. An expression that starts with a quote must be quoted in YAML, e.g., `diskSelector: "'/dev/disk/by-id/md-name-talos:boot' in disk.symlinks"`. When a disk selector matches more than one disk, Omni selects the first regular disk by path. A disk built on top of other disks, such as an MD RAID array, is selected only when it is the only match. Installing Talos to an MD RAID array requires Talos v1.14 or later. Create the array with the config patches in [Boot from a RAID1 array](https://docs.siderolabs.com/talos/v1.14/configure-your-talos-cluster/storage-and-disk-management/raid.md#boot-from-a-raid1-array). Select it as the install disk with a disk selector instead of the `UnattendedInstallConfig` document shown there, which Omni does not accept. ## Check the install disk of a machine Omni stores the install disk it uses for each machine in the `MachineInstallDiskStatus` resource: ```bash theme={null} omnictl get machineinstalldiskstatuses -o yaml ``` ```yaml theme={null} spec: disk: /dev/nvme0n1 message: selected by the install disk selector disks: - devpath: /dev/nvme0n1 selectable: true skipreason: "" members: [] - devpath: /dev/md0 selectable: true skipreason: built on top of other disks members: - sdb - sdc - devpath: /dev/sdb selectable: false skipreason: a member of /dev/md0 members: [] ``` * `disk`: the install disk. It is empty when no disk can be used. * `message`: why `disk` is empty, or how the disk was selected. * `disks`: every disk of the machine. `selectable` says whether the UI offers the disk, and `skipreason` says why the automatic selection skips it. When `disk` is empty, Omni does not generate the configuration of the machine, so the machine waits in its cluster. Check the `message` field to see why, e.g., `no disk matches the install disk selector`. The resource carries the cluster label of the machine, so you can list the install disks of a cluster. Replace `` with the name of the cluster: ```bash theme={null} omnictl get machineinstalldiskstatuses -l omni.sidero.dev/cluster= ``` This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.