22.2. Enabling/Disabling Write Barriers

To mitigate the risk of data corruption during power loss, some storage devices use battery-backed write caches. Generally, high-end arrays and some hardware controllers use battery-backed write caches. However, because the cache's volatility is not visible to the kernel, Red Hat Enterprise Linux 6 enables write barriers by default on all supported journaling file systems.
For devices with non-volatile, battery-backed write caches and those with write-caching disabled, you can safely disable write barriers at mount time using the -o nobarrier option for mount. However, some devices do not support write barriers; such devices will log an error message to /var/log/messages (refer to Table 22.1, “Write barrier error messages per file system”).

Table 22.1. Write barrier error messages per file system

File SystemError Message
ext3/ext4JBD: barrier-based sync failed on device - disabling barriers
XFSFilesystem device - Disabling barriers, trial barrier write failed
btrfsbtrfs: disabling barriers on dev device

Note

The use of nobarrier is no longer recommended in Red Hat Enterprise Linux 6 as the negative performance impact of write barriers is negligible (approximately 3%). The benefits of write barriers typically outweigh the performance benefits of disabling them. Additionally, the nobarrier option should never be used on storage configured on virtual machines.