Re: [ext4] Documentation patch

From: Theodore Tso
Date: Sat Dec 06 2008 - 17:26:11 EST

This is what I have added to the ext4 patch queue.

- Ted

Update Documentation/filesystems/ext4.txt

Fix paragraph with recommendations on how to tune ext4 for benchmarks.

Signed-off-by: "Theodore Ts'o" <tytso@xxxxxxx>
diff --git a/Documentation/filesystems/ext4.txt b/Documentation/filesystems/ext4.txt
index 845e691..19bb93f 100644
--- a/Documentation/filesystems/ext4.txt
+++ b/Documentation/filesystems/ext4.txt
@@ -58,13 +58,18 @@ Note: More extensive information for getting started with ext4 can be

# mount -t ext4 /dev/hda1 /wherever

- - When comparing performance with other filesystems, remember that
- ext3/4 by default offers higher data integrity guarantees than most.
- So when comparing with a metadata-only journalling filesystem, such
- as ext3, use `mount -o data=writeback'. And you might as well use
- `mount -o nobh' too along with it. Making the journal larger than
- the mke2fs default often helps performance with metadata-intensive
- workloads.
+ - When comparing performance with other filesystems, it's always
+ important to try multiple workloads; very often a subtle change in a
+ workload parameter can completely change the ranking of which
+ filesystems do well compared to others. When comparing versus ext3,
+ note that ext4 enables write barriers by default, while ext3 does
+ not enable write barriers by default. So it is useful to use
+ explicitly specify whether barriers are enabled or not when via the
+ '-o barriers=[0|1]' mount option. When tuning ext3 for best
+ benchmark numbers, it is often worthwhile to try changing the data
+ journaling mode; '-o data=writeback,nobh' can be faster for some
+ workloads. A large journal can also be helpful for
+ metadata-intensive workloads.

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