What should a technician procure to upgrade a server hard disk from 40GB to 136GB if it supports up to 15000rpm?

The correct choice is to procure a 136GB SAS interface storage device for upgrading the server's hard disk. SAS (Serial Attached SCSI) is designed for enterprise-level storage solutions and is particularly well-suited for server environments due to its high-performance capabilities. It supports faster data transfer speeds and provides better reliability and redundancy than other interfaces, making it ideal for critical applications that require maximum uptime and speed.

In addition, SAS drives typically support higher rotational speeds, such as up to 15,000 RPM, which aligns with the specifications required for this server upgrade. This characteristic enhances the performance of the server, especially for data-intensive tasks, and takes advantage of the higher throughput that SAS technology offers.

Other interfaces, such as SATA, are generally more cost-effective and suitable for consumer applications; however, they do not provide the same level of performance or enterprise reliability as SAS. USB and FireWire interfaces are primarily meant for external storage solutions and are not appropriate for server upgrades where internal storage performance is critical. Therefore, choosing the SAS interface storage device is the most appropriate option for upgrading the server's hard disk in this scenario.