Chapter 5. Storage
Enhancements to device-mapper
Several significant enhancements to
device-mapper have been introduced in Red Hat Enterprise Linux 6.6:
- The
dm-cachedevice-mapper target, which allows fast storage devices to act as a cache for slower storage devices, has been added as a Technology Preview.
- The device-mapper-multipath ALUA priority checker no longer places the preferred path device in its own path group if there are other paths that could be used for load balancing.
- The
fast_io_fail_tmoparameter in themultipath.conffile now works on iSCSI devices in addition to Fibre Channel devices. - Better performance can now be achieved in setups with a large number of multipath devices due to an improved way in which the device-mapper multipath handles sysfs files.
- A new
force_syncparameter inmultipath.confhas been introduced. The parameter disables asynchronous path checks, which can help limit the number of CPU contention issues on setups with a large number of multipath devices.
dm-era Technology Preview
The device-mapper-persistent-data package now provides tools to help use the new
dm-era device mapper functionality released as a Technology Preview. The dm-era functionality keeps track of which blocks on a device were written within user-defined periods of time called an era. This functionality allows backup software to track changed blocks or restore the coherency of a cache after reverting changes.
