----- Original Message -----
From: "George Wilson"
I think there is probably another way we can solve this problem but I
first want to get a better understanding of the corruption. We have not
integrated the TRIM support upstream and I suspect that's the source of
most of the problems. Can you confirm that with TRIM disabled that most
of corruption you've seen does not occur? I'm trying to get context here
since we've not seen this type of failure elsewhere.
In the case of TRIM if BIO delete's are disabled the free IO's don't get
sent to physical media and instead instantly return ZIO_PIPELINE_CONTINUE.
static int
vdev_geom_io_start(zio_t *zio)
{
...
switch (zio->io_type) {
case ZIO_TYPE_FREE:
if (vdev_geom_bio_delete_disable)
return (ZIO_PIPELINE_CONTINUE);
}
}
Since I'm not familiar with the TRIM implementation in FreeBSD I was
wondering if you could explain the scenario that leads to the
corruption. The fact that the pipeline doesn't allow the zio to change
mid-pipeline is actually intentional so I don't think we want to make a
change to allow this to occur. From code inspection it does look like
the vdev_*_io_start() routines should never return
ZIO_PIPELINE_CONTINUE. I will look at this closer but it looks like
there is a bug there.
When I looked there few cases where this can happen for example scrubbing
reads in mirror, unreadable devices for file IO's.
Anyway, if you could give me more details to the corruption I would be
happy to help you design a way that this can be implemented while still
ensuring that a zio cannot change while the pipeline is still active.
Thanks for diving into this and I will post more about the bugs that
look to exist in the vdev_*_io_start() routines.
Given how queuing can execute a different IO than was passed in by
zio_execute to the pipeline I don't think its a valid to assume that
IO's can't return continue without asserting otherwise.
Regards
Steve
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