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22.2. Enabling and 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 7 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 log an error message to /var/log/messages. For more information, see Table 22.1, “Write Barrier Error Messages per File System”.
Table 22.1. 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 |
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