problems with gmirror on ggate over slow link

[Pete French]

I am using 7.1-STABLE from a few days ago on all amchines, but this
has been going on a while. Very simply I am mirroring together a pair
of discs, one local, one remote. The remote disc is accessed using ggate.

If the remote diisc is actually on a very close machine - e.g. a server
plugged into the same ether net - then all works fine. If I make
the remote disc somewhere actually substantially further away on the
nbetwork, however, then when I attach the disc it starts to rebuild the
mirror but then fails a fraction of a second later thus:

GEOM_MIRROR: Device mysql0: rebuilding provider ggate1a.
GEOM_MIRROR: Synchronization request failed (error=5). ggate1a[WRITE(offset=1310720, length=131072)]
GEOM_MIRROR: Device mysql0: provider ggate1a disconnected.
GEOM_MIRROR: Device mysql0: rebuilding provider ggate1a stopped.

The interesting this is that the problem is only with gmirror, not with
the underlying ggate disc which remains attached and accessible. I tested
this by adding a second partition (ggate1b in the example above) and
mounting a UFS filesystem on that.

My conjecture would be that a buffer somewhere is filling up, and
instead of gmirror waiting for it, instead it just fails the write.

Any ideas ? Is this actually a bug ?

-pete.