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16.2. 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 cached. However, because the cache's volatility is not visible to the kernel, Fedora 14 enables write barriers by default on all supported journaling file systems.

Note

Write caches are designed to increase I/O performance. However, enabling write barriers means constantly flushing these caches, which can significantly reduce performance.
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 16.1, “Write barrier error messages per file system”).
Table 16.1. Write barrier error messages per file system
File System Error Message
ext3/ext4 JBD: barrier-based sync failed on device - disabling barriers
XFS Filesystem device - Disabling barriers, trial barrier write failed
btrfs btrfs: disabling barriers on dev device