> > Specificly, I am looking at the Adaptec RAID controllers and their i2o drivers. I am told
> the
> > kernel's i2o driver lacks a strong guarantee on fsync, and so far am unable to determine if
> the
> > dpt_i2o driver also falls short in this reguard.
>
> Only dpt can tell you what their firmware actually does.
Yeah, I wasn't so much interrested in the firmware just yet, just interrested if the device driver
(dpt_i2o) gave it a fighting chance of doing the right thing.
> The i2o core drivers use the following rules
> i2o_block by default assumes the card is caching. It adopts write
> through mode if the controller has no battery, write back if it shows
> battery. This can be configured differently via ioctls including the
> ability to tune write through of large I/O's (to avoid cache thrashing),
> and to do write back with no battery backup for performance in cases
> where losing the data on a crash doesn't matter (eg swap)
That's what I read in the comments too, but looking at the code I only ever see it set to
write-back. I verified this with blktool - our controllers have no battery, and blktool showed
the i2o-wcache state as write-back.
However, I was also told that the i2o_block driver lacks barrier support, so even in the
write-back case, the controller won't be told to flush/sync.
I was sent a patch against 2.6.10 that implements barrier support in i2o_block, but the code base
has shifted too much for me to make it apply.
-Kenny
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