Improve mg_aliquot math

When calculating mg_aliquot alike to #12046 use number of unique data
disks in the vdev, not the total number of children vdev.  Increase
default value of the tunable from 512KB to 1MB to compensate.

Before this change each disk in striped pool was getting 512KB of
sequential data, in 2-wide mirror -- 1MB, in 3-wide RAIDZ1 -- 768KB.
After this change in all the cases each disk should get 1MB.

Reviewed-by: Brian Behlendorf <[email protected]>
Reviewed-by: Ryan Moeller <[email protected]>
Signed-off-by: Alexander Motin <[email protected]>
Sponsored-By: iXsystems, Inc.
Closes #13388 

0 files changed, 0 insertions, 0 deletions