On Wed, Feb 25, 2009 at 12:45:11PM -0800, Tracy Reed wrote:
> On Wed, Feb 25, 2009 at 03:36:36PM -0500, Ed Cashin spake thusly:
> > preserved reliably. Although it's true that there's only one page
> > cache, the buffers of each vblade process are independent.
>
> Ah. Good point. Any way to make the one vblade process listen on
> multiple interfacse? Would that solve this issue?
If I understand the issue correctly then no, that won't change anything.
Both the network, the NIC and the kernel may re-order packets arriving
on different interfaces wrt. each other, so listening on multiple
interfaces won't give you any extra ordering guarantees.
If you want to access the same same target from the same initiator via
multiple paths, then the initiator's kernel will ensure that there are
no overlapping requests, and the target's kernel will ensure that the
different vblade processes have a consistent view of the device's
contents (except if one of the vblade processes is configured to use
direct I/O while the other is not, but if you do such thing then you
deserve what you get).
If you want to access the same target from different initiators, then
the initiators must use some form of distributed locking to ensure they
do not step on each other's toes; no amount of hacking on the vblade
side can substitute that.
Gabor
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MTA SZTAKI Computer and Automation Research Institute
Hungarian Academy of Sciences
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