fsync, ext3, raid (md) 1, write barriers and PATA caching

Bruno Wolff III bruno at wolff.to
Sat Dec 9 22:04:59 UTC 2006

I have been trying to figure out whether I can enable write caching on my
PATA hard drives (WD3200JB) and have fsync not return until data is
safely on the platters. I am also running software raid.
This is currently on FC5 (though soon to be FC6) with a 2.6.18 kernel.

>From snippets I have found on the net, it looks like write barriers are
pushed down through software raid when using raid 1. So that if I mount
the file systems with data=ordered and barrier=1, I think I should be
OK, but I was hoping to get a more definitive answer.

It also looks like barrier=1 is or will be the default for ext3. Is there
a way I can check if this is the case on my system?

/proc/mounts doesn't show the barrier option when I use barrier=1 or don't
specify it at all. mount -lv shows the barrier option (when it was used
for mounting), but not the data option. I am not sure if either of these
are using the same data that the ext3 driver is using.

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