Up until now the default io scheduler was set in kernel arguments.
This is dangerous, intrusive, unportable and indeterministic.

bug#754334 added tuned dependency which should have done exactly this, but as it turns out (bug#878511) it does not applies the policy dynamically.

So we need some solution within vdsm or bootstrap. A solution for vdsm is available at[1].

But as tuned entered the picture it may be wiser to perform this at bootstrap level, dropping it when tuned is ready.

[1] http://gerrit.ovirt.org/#/c/8700/