Because of the varying sizes/types of HDs in the question and that is requests end users to see ALL the drives within JBOD would be a better selection than RAID. With a RAID it would appear as one logical unit and the varying sizes would have a limit of the smaller disks used.
https://www.techtarget.com/searchstorage/definition/JBOD

Explanation
The solution the administrator implemented extended runtime. Runtime is the amount of time that a UPS can provide backup power to a server in case of a power outage. By installing additional batteries in the UPS, the administrator increased the capacity and duration of the backup power, allowing the server more time to shut down properly.
References: CompTIA Server+ SK0-005 Certification Study Guide, Chapter 1, Lesson 1.4, Objective 1.4

Explanation
Cloud IaaS (Infrastructure as a Service) is a service model that allows users to rent virtualized computing resources over the internet, such as servers, storage, network, and software. Cloud IaaS can provide several benefits for disaster recovery and failover scenarios, such as:
Lower cost: Cloud IaaS can reduce the capital and operational expenses of building and maintaining a physical disaster recovery site, as users only pay for the resources they use on demand12.
Scalability: Cloud IaaS can offer flexible and elastic scalability of resources, as users can easily provision or deprovision resources according to their needs and workload12.
Availability: Cloud IaaS can ensure high availability and reliability of the application, as users can leverage the cloud provider's redundant and geographically distributed infrastructure12.
Simplicity: Cloud IaaS can simplify the failover process, as users can use the cloud provider's tools and services to automate and orchestrate the failover operations12.
Therefore, building a cloud IaaS and performing a failover of the application would be the most cost-effective solution for the company, as it would allow them to simulate a failover of a critical application on production configurations and IP address schemes without investing in a physical disaster recovery site.

Explanation
To comply with the user requirements, the best options are to install the OS on a RAID 1 array, configure RAID 5 for the application data, and use SSD hard drives for the data application array. Here is why:
RAID 1 is a mirroring technique that creates an exact copy of data on two disks. This provides redundancy and fault tolerance in case of hard drive failure. RAID 1 also improves read performance since either disk can be read at the same time. Therefore, installing the OS on a RAID 1 array meets the first requirement of separating the OS from the application data and protecting it from hard drive failure.
RAID 5 is a striping technique with parity that distributes data and parity blocks across three or more disks. This provides improved performance and storage efficiency compared to RAID 1, as well as fault tolerance in case of a single disk failure. Therefore, configuring RAID 5 for the application data meets the second and third requirements of providing high IOPS performance and data availability.
SSD hard drives are solid-state drives that use flash memory to store data. They have no moving parts and offer faster read and write speeds, lower latency, and lower power consumption than traditional HDDs. Therefore, using SSD hard drives for the data application array meets the second requirement of providing high IOPS performance.
References:
https://phoenixnap.com/kb/raid-levels-and-types
https://en.wikipedia.org/wiki/Standard_RAID_levels

A warm site is a backup site that has some of the necessary hardware, software, and network resources to resume operations, but not all of them. A warm site requires some time and effort to become fully operational. A warm site is different from a cold site, which has minimal or no resources, and a hot site, which has all the resources and is ready to take over immediately.