External journal on flash drive

Stephen C. Tweedie sct at redhat.com
Tue Sep 14 10:40:04 UTC 2004


On Mon, 2004-09-13 at 23:39, Mika Liljeberg wrote:

> > > 2) Currently, the main drive seems to spin up within 60 seconds after a
> > > write access.
> > That's not related to journal activity --- that's normal writeback.

> Ah, I see. Does this also hold for data_journal mode?

Yes.  You can tune the bdflush parameters to tweak the 60 second

> Sounds like my best bet would be to have my filesystems in data_journal
> mode

I'd rather go with data=ordered; flash isn't the fastest of media, and
you have much more journal traffic with data=journal.  And in
data=ordered, if you ...

> configure the bdflush parameters to delay writeback as much
> as possible

...then you should be able to avoid the spinups.

> . If I understand correctly, that should allow for maximal
> spin down times and still maintain full data integrity after a crash.
> For ext3 filesystems, anyway. :-|

data=ordered (the default) already preserves full data integrity after a
crash.  It's only data=writeback which relaxes the integrity guarantees.


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