Working with write barriers and journaling filesystems

IMPOSING ORDER

Article from Issue 78/2007
Author(s):

Your journaling filesystem is carefully tracking write operations – but what happens when the data gets to the disk? A write barrier request can help protect your data.

Journaling filesystems offer some important benefits for the user, but they also pose some subtle problems. One problem is that the filesystem must keep a record that reflects the state of write operations to the storage device, but the storage device may actually change the order of those write requests in an effort to optimize performance. If the system fails at a point where the journal is out of step with the true sequence of write operations, your data may not be as safe as you think.

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