Bruno Wolff III wrote:
> On Tue, Jun 10, 2008 at 09:49:16 -0500,
> Eric Sandeen <sandeen@xxxxxxxxxx> wrote:
>> LVM barriers aren't so much broken as simply un-implemented by design.
>>
>> static int dm_request(struct request_queue *q, struct bio *bio)
>> {
>> ...
>> /*
>> * There is no use in forwarding any barrier request since we can't
>> * guarantee it is (or can be) handled by the targets correctly.
>> */
>
> That seems weird. I thought one of the reasons for having stacked block devices
> is that you could pass on barrier requests.
Not really; in general it is trickier w/ more devices I think.
md for example passes barriers on raid1 but not 0 or 5 AFAIK...
> I have seen comments about adding barrier support to linear block devices
> that currently don't support it (e.g. dmcrypt) relatively recently.
>
> On a somewhat related note there was a discussion about issues with barriers
> on lmkl last February that suggested there are issues with sync on linux
> if you have write cache enabled even if you are using barriers.
Got a url?
Thanks,
-Eric
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