data=writeback
also: writeback mode, journal=writeback
A journaling mode for ext3/ext4 filesystems that only logs filesystem metadata (not file data) to the journal, offering faster performance but less data safety after a crash.
data=writeback is a journaling mode that balances performance and safety by journaling only metadata changes, not the actual file contents. When you write data, the filesystem notes the structural changes in its journal but writes file data directly to disk without journal protection.
After an unexpected crash or power loss, the journal can restore the filesystem's structural integrity, but file data written just before the crash may be corrupted or lost. For this reason, data=writeback is faster than data=ordered (the default) but riskier for critical data.
Example: Mount an ext4 filesystem in writeback mode with mount -o data=writeback /dev/sda1 /mnt. This is commonly used for high-performance systems where some data loss is acceptable, such as caching servers or temporary storage.