Write barrier support in ext3

[Martin Steigerwald]

Hello ext3 users and developers,

I am gathering information for an article about journal filesystems with 
emphasis on write barrier functionality, how it works, why journalling 
filesystems need write barrier and the current implementation of write 
barrier support for different filesystems. 

Background of this is my own experience of three XFS crashes in one week:
http://bugzilla.kernel.org/show_bug.cgi?id=6380

With 2.6.17.1 XFS seems to works stable with write caches after applying a 
(write cache unrelated) fix:
http://bugzilla.kernel.org/show_bug.cgi?id=6757

But I like to provide information on ext3, jfs, reiserfs 3 and reiser 4 as 
well.

I like to ask you:

1) Since which kernel release are write barriers officially supported and 
stable in ext3? Is it 2.6.16? I found the barrier option in 
filesystem/ext3.txt in my 2.6.17 kernel.

2) Since which kernel release are write barriers enabled by default in 
ext3 if any ?

3) Are there any performance measurements for ext3? It is expected that 
write barrier will be slower than no write barrier but faster then 
disabled write caches. 

4) Have there been any issues regarding write barrier support in ext3 that 
are worth to mention in the article?

If you have any links of relevant information pieces, please share them 
with me. Nonetheless I will continue grepping kernel changelogs and the 
internet for until I have the information I want for that article.

Please CC to me personally as I am not subscribed to the list...

Regards,
-- 
Martin 'Helios' Steigerwald - http://www.Lichtvoll.de
GPG: 03B0 0D6C 0040 0710 4AFA  B82F 991B EAAC A599 84C7