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cache+barriers vs cache+nobarriers vs disabled cache+barriers vs disable

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Subject: cache+barriers vs cache+nobarriers vs disabled cache+barriers vs disabled cache+nobarriers
From: "Leon Kolchinsky" <leonk@xxxxxxxxxxxxxxxxxxxxx>
Date: Thu, 15 Mar 2007 11:16:38 +0200
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Hello All,


After reading http://oss.sgi.com/projects/xfs/faq.html#wcache 
and some posts on the list I've got the following question:

If I have disabled write cache on the disk (hdparm -W0 /dev/hda) and by
default FS is mounted with "barrier" enabled, Is there any taste in enabling
"barrier"(by default) because write cache is disabled anyway or may be it's
a good idea to mount with "nobarriers" in this case?

Or may be I'm wrong here and write cache has nothing to do with "barrier"
option?

I thought that "barrier" is on by default to somewhat minimize potential
dangers of enabled write cache? But if write cache is disabled, would
"barrier" option just slow down the FS performance (which is already slowed
down by "hdparm -W0 /dev/had" anyway)?

Any inside wisdom on the subject of this mail would be much appreciated :)



Best Regards,
Leon Kolchinsky




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