2.6. Physical Storage
2.6.1. Changed mount behavior at boot
nofailoption, as shown.
/dev/essential-disk /essential xfs auto,defaults 0 0 /dev/non-essential-disk /non-essential xfs auto,defaults,nofail 0 0
2.6.2. Using LVM snapshots as a rollback mechanism
- Add another disk. Instructions can be found in the Red Hat Enterprise Linux 7 Storage Administration Guide, available from http://access.redhat.com/site/documentation/Red_Hat_Enterprise_Linux/.
- Use parted to check for free space that is not allocated to an existing partition.
- Use lsblk to check for empty partitions, or partitions that can be deleted to free space.
- Use vgdisplay to check for free space in a volume group that is not allocated to a logical volume.
- Use df to check for file systems that have free space and can be reduced, so that their logical volume or partition can be shrunk to free space.
- Snapshot size is not adjusted automatically. If your snapshot gets too large for its partition, it may become invalid, and rollback will fail. It is therefore imperative to allocate a sufficiently large space for a snapshot of your entire system, before creating that snapshot. If you need to resize a root snapshot, you will need an additional device such as a Live CD that can be used as a root device while your original root device is unmounted and resized.
- The copy-on-write device of a snapshot is not mirrored, and will be on a single device regardless of whether your system is mirrored. If the device fails and you lose the snapshot, rollback is impossible. Red Hat recommends using a physical volume with mdraid, or using multiple snapshots to separate disks. Using multiple snapshots is slower.
- In the event of a crash during installation, the system can become impossible to boot. In this circumstance, Red Hat recommends booting with a Live CD or PXE boot and merging your snapshot when the system has booted successfully. Merging instructions are available in the Red Hat Enterprise Linux 7 LVM documentation, available from http://access.redhat.com/site/documentation/Red_Hat_Enterprise_Linux/.
- Rollback returns
/var/logto the state it was in prior to upgrade. For auditing purposes, Red Hat recommends copying log files from installation to a separate location prior to initiating rollback.
2.6.3. Target Management with targetcli
2.6.4. Persistent Device Names
/dev/disk/by-*/) in kernel messages. This lets the system administrator identify the messages associated with a device, even if the device name changes from boot-to-boot.
/dev/kmsglog, which can be displayed with the
dmesgcommand, now shows the messages for the symbolic links, which
udevhas created for kernel devices. These messages are displayed in the following format:
udev-alias: device_name (symbolic_link symbolic link ...). For example:
udev-alias: sdb (disk/by-id/ata-QEMU_HARDDISK_QM00001)
udev.alias=1to the kernel command line in
2.6.5. LVM cache volumes
lvmcachemanual page for information on creating cache logical volumes.