| Message ID | 8763m3u9kv.fsf@basilikum.skogtun.org |
|---|---|
| State | Superseded, archived |
| Headers | show |
On Mon, Dec 01, 2008 at 05:46:56PM +0100, Harald Arnesen wrote: > So when comparing with a metadata-only journalling filesystem, such > - as ext3, use `mount -o data=writeback'. And you might as well use > + as jfs or xfs, use `mount -o data=writeback'. And you might as well use data=ordered comes closest to what xfs does for quite a long time.. -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Christoph Hellwig wrote: > On Mon, Dec 01, 2008 at 05:46:56PM +0100, Harald Arnesen wrote: >> So when comparing with a metadata-only journalling filesystem, such >> - as ext3, use `mount -o data=writeback'. And you might as well use >> + as jfs or xfs, use `mount -o data=writeback'. And you might as well use > > data=ordered comes closest to what xfs does for quite a long time.. Agreed; that whole bit which mentions other filesystem comparisons should probably be stricken, unless it can be proven/demonstrated/substantiated that ext3 really does "offer higher data integrity guarantees than most" at this point. data=ordered ensures that stale data won't be exposed on a crash; xfs won't do this (it'd be a security bug) and I'd be surprised if jfs or reiserfs do either. And it probably *should* be mentioned that data=writeback bears this risk. And until ext3 turns on barriers by default, I don't think it's fair to talk too much about integrity guarantees. :) -Eric -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Mon, Dec 01, 2008 at 11:58:52AM -0600, Eric Sandeen wrote: > Christoph Hellwig wrote: > > On Mon, Dec 01, 2008 at 05:46:56PM +0100, Harald Arnesen wrote: > >> So when comparing with a metadata-only journalling filesystem, such > >> - as ext3, use `mount -o data=writeback'. And you might as well use > >> + as jfs or xfs, use `mount -o data=writeback'. And you might as well use > > > > data=ordered comes closest to what xfs does for quite a long time.. > > Agreed; that whole bit which mentions other filesystem comparisons > should probably be stricken, unless it can be > proven/demonstrated/substantiated that ext3 really does "offer higher > data integrity guarantees than most" at this point. > > data=ordered ensures that stale data won't be exposed on a crash; xfs > won't do this (it'd be a security bug) and I'd be surprised if jfs or > reiserfs do either. And it probably *should* be mentioned that > data=writeback bears this risk. Well, the original text was written by David Kleikamp, so it might be the case that jfs doesn't handle the stale data block case well. I haven't checked. However, the sense of that paragraph got mangled badly in commit 93e3270c, and what's there clearly doesn't make any sense. I agree the best thing to do is to nuke that whole paragraph. The one thing that's worth mentioning (as a replacement paragraph) is that ext4 (and many other filesystems) has barreiers on by default, and ext3 has barriers off by default, so that's something that should be taken into account when doing head-to-head comparisons. - Ted P.S. Speaking of barriers, there was a rumor floating around that someone was working on patches so at least in the case of RAID 0 and RAID 1, that the LVM and MD stack would actually pass barier requests down to the block device layer. Whatever happened to that? Is that bug in the LVM layer going to get fixed any time soon? -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
======================================================================== diff --git a/Documentation/filesystems/ext4.txt b/Documentation/filesystems/ext4.txt index 174eaff..5bbe79e 100644 --- a/Documentation/filesystems/ext4.txt +++ b/Documentation/filesystems/ext4.txt @@ -61,7 +61,7 @@ Note: More extensive information for getting started with ext4 can be - 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 + as jfs or xfs, 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.
My first patch, hope it goes through ok! Applies to 2.6.28-rc6-00184-gd9d060a. Compare ext4's journalling with anything but ext3's. These use the same journalling modes, most other Linux filesystems do only metadata journalling. Signed-off-by: Harald Arnesen <harald@skogtun.org>