1V0-621 · Question #238
How does Storage I/O Control protect the service level of critical virtual machines?
The correct answer is A. Gives preferential I/O resource allocation to critical virtual machines. See the full explanation below for the reasoning.
Question
How does Storage I/O Control protect the service level of critical virtual machines?
Options
- AGives preferential I/O resource allocation to critical virtual machines
- BAllocates I/O resources equally among all virtual machines
- CMonitors the storage habits of the virtual machines
- Dtakes a count of virtual machines on the storage device
How the community answered
(16 responses)- A81% (13)
- B13% (2)
- C6% (1)
Community Discussion
5
Brenda K.Jun 26, 2026A is correct. Storage I/O Control kicks in when a datastore hits a congestion threshold and then doles out I/O based on shares and limits, so VMs with higher priority settings get more throughput when things get tight, not a flat equal split like B says.
Yelena W.Jun 11, 2026A is right, SIOC queues I/O shares so critical VMs win during contention.
Mei-Ling H.Jun 13, 2026Right, but watch the wording on the exam, because SIOC only starts enforcing those shares once the datastore hits the congestion threshold (default 30 ms latency), so outside of contention the shares do nothing.
Mei-Ling H.Jun 14, 2026I keep coming back to C on this one because the word "protect" in the stem is really asking what mechanism SIOC uses, and you cannot protect anything without first monitoring it. If the system does not watch the storage behavior of the VMs, it has no baseline to work from, so monitoring the storage habits is logically the first and core function. The other options like A sound plausible but "preferential allocation" feels more like what you would describe for Storage DRS or shares and limits configured manually, not specifically SIOC. Option C also fits the passive, observational nature of a control mechanism that kicks in only when congestion is detected, which means it is sitting there watching habits before it does anything else. Until I see a clearer reference in the official VMware documentation that explicitly ties SIOC to preferential allocation rather than monitoring-based control, I am staying with C.
Brenda K.Jun 17, 2026Mei-Ling, monitoring is part of how SIOC detects congestion, but the mechanism that actually protects VMs is preferential I/O allocation via shares, which is exactly what option A describes, and that is confirmed in VMware's own SIOC documentation as the primary control action once the latency threshold is crossed.