Speedup is hard to measure because the only time vdev_geom_open_by_guids
gets called on many drives at the same time is during boot. But with
vdev_geom_open hacked to always call vdev_geom_open_by_guids, operations
like "zpool create" speed up by 65%.
sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_geom.c
* Read all of a vdev's labels in parallel instead of sequentially.
* In vdev_geom_read_config, don't read the entire label, including
the uberblock. That's a waste of RAM. Just read the vdev config
nvlist. Reduces the IO and RAM involved with tasting from 1MB to
448KB.
Reviewed by: avg
MFC after: 4 weeks
Sponsored by: Spectra Logic Corp
Differential Revision: https://reviews.freebsd.org/D6153
1ca5fbab55