Linux Storage and Filesystem workshop, day 1 [LWN.net]

Linux Storage and Filesystem workshop, day 1

Posted Apr 8, 2009 1:22 UTC (Wed) by pr1268 (subscriber, #24648)
Parent article: Linux Storage and Filesystem workshop, day 1

[After writing the above, your editor noticed that Linus had just merged a change to make data=writeback the default for ext3 in 2.6.30. Your editor, it seems, is easily surprised.]

I'm surprised, also. And a little disappointed. After all, data=ordered has worked fine for, what, 7 1/2 years now?

If it ain't broke, don't fix it. I'll be modifying my fstab files accordingly. </grumble>

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journal_data_ordered

Posted Apr 8, 2009 3:44 UTC (Wed) by pr1268 (subscriber, #24648) [Link]

Thanks! But, I'm curious: If I specify journal_data_ordered in tune2fs(8), and I put data=writeback in /etc/fstab, which mode actually gets used?

journal_data_ordered

Posted Apr 8, 2009 3:57 UTC (Wed) by bojan (subscriber, #14302) [Link]

I think the one from /etc/fstab. The manual of tune2fs says:

-o [^]mount-option[,...]
Set or clear the indicated default mount options in the filesystem.

I take this to mean that if you have "defaults" in /etc/fstab, then the FS option can specify what is the default for that particular file system. I would think the default would get overridden by an explicit mount option from /etc/fstab though.

But, that's easy to check. Just set the options on the FS level and/or fstab, mount and check dmesg to see what really happened.

journal_data_ordered

Posted Apr 8, 2009 5:11 UTC (Wed) by butlerm (subscriber, #13312) [Link]

The default spoken of is a kernel level default that applies prior to and
in the absence of any user specified mount options. In other words, if you
specify data=writeback on any supporting filesystem, that is what you will
get.

journal_data_ordered

Posted Apr 8, 2009 5:18 UTC (Wed) by butlerm (subscriber, #13312) [Link]

My tune2fs(8) man page states:

"-o [mount_option,...]

Set or clear the indicated default mount options in the filesys-
tem. Default mount options can be overridden by mount options
specified either in /etc/fstab(5) or on the command line argu-
ments to mount(8). Older kernels may not support this feature;"

There are really three "defaults" of course. The filesystem implementation
level, the filesystem image level, and the /etc/fstab level, in that order.

journal_data_ordered

Posted Apr 8, 2009 7:13 UTC (Wed) by bojan (subscriber, #14302) [Link]

Gee - thanks! I really am blind. My manual page says exactly the same thing (of course)...