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9.13.4.  Create a Btrfs subvolume

Btrfs is still experimental

Fedora 18 includes Btrfs as a technology preview to allow you to experiment with this file system. You should not choose Btrfs for partitions that will contain valuable data or that are essential for the operation of important systems.
Btrfs is a type of file system, but has several features characteristic of a storage device. It is designed to make the file system tolerant of errors, and to facilitate the detection and repair of errors when they occur. It uses checksums to ensure the validity of data and metadata, and maintains snapshots of the file system that can be used for backup or repair.
During manual partitioning, you will create Btrfs subvolumes rather than volumes. The installer then automatically creates a Btrfs volume to contain these subvolumes. The sizes reported for each Btrfs mount point in the left pane of the Manual Partitioning screen will be identical because they reflect the total size of the volume rather than each individual subvolume.
Configure a Btrfs volume
The area of the Manual Partitioning screen for configuring a Btrfs subvolume.
Figure 9.23. Configure a Btrfs volume

To create a Btrfs subvolume:
  1. Create a partition as described in Section 9.13.1, “Adding and Configuring Partitions”. Configuring this partition will configure the Btrfs subvolume.
  2. Click the Device Type dropdown menu and select BTRFS.
  3. Two checkboxes will appear beneath the File System dropdown menu, which is grayed out for Btrfs. If you want to add a RAID level to the subvolume, choose one by checking the required boxes. If not, skip to step 5.
    Next to each checkbox, any disk space that will be gained or lost by selecting that option will be displayed in red. Certain boxes may be grayed out and labeled not enough disks if that RAID level cannot be achieved with the available disks.
    The checkboxes required for each RAID level are:
    Optimized performance (stripe) = RAID0
    Distributes data across multiple storage devices. Level 0 RAIDs offer increased performance over standard partitions, and can be used to pool the storage of multiple devices into one large virtual device. Note that Level 0 RAIDS offer no redundancy and that the failure of one device in the array destroys the entire array. RAID 0 requires at least two RAID partitions.
    Redundancy (mirror) = RAID1
    Mirrors the data on one storage device onto one or more other storage devices. Additional devices in the array provide increasing levels of redundancy. RAID 1 requires at least two RAID partitions.
    Redundancy (mirror) and Optimized performance (stripe) = RAID10
    Level 10 RAIDs are nested RAIDs or hybrid RAIDs. Level 10 RAIDs are constructed by distributing data over mirrored sets of storage devices. For example, a level 10 RAID constructed from four RAID partitions consists of two pairs of partitions in which one partition mirrors the other. Data is then distributed across both pairs of storage devices, as in a level 0 RAID. RAID 10 requires at least four RAID partitions.


    If both Redundancy (mirror) and Optimized performance (stripe) are checked but only two disks are included in the RAID device (refer to step 4), the resulting device will have a RAID 1 rather than RAID 10 level of data security. A genuine RAID 10 device will only be created if four disks are included. If you still choose to create a level 10 RAID with only two disks, you can add additional disks and make other RAID modifications after installation using the mdadm utility.
  4. Keeping the partition selected in the left-hand pane, select the configuration button below the pane to open the Configure Mount Point dialog. Select which disks will be included as part of the RAID on the subvolume and click Select.
    If fewer disks are included than the specified RAID level needs, a yellow notification bar at the bottom of the screen will inform you that Device reconfiguration failed. Clicking this warning prompts a dialog informing you how many disks are required.
  5. Click Apply Changes to save your changes, and either continue with another partition or click Finish Partitioning to return to the Installation Summary Menu.


Placing /boot on a Btrfs subvolume may lead to instability and is not recommended.