A GIS administrator receives reports of slow-performing services and notices that disk space is filling up after recent troubleshooting sessions. In…

Setting the ArcGIS Server log level to Debug causes the system to generate highly detailed and voluminous log files for all server activities. This action has two primary consequences that match the reported issues. First, the constant and intensive disk I/O operations required to write these extensive logs consume significant system resources (CPU and disk throughput), leading to slower service performance. Second, the large volume of log data generated rapidly consumes disk space. This single action directly explains both of the symptoms observed by the administrator.

A. Additional services in the shared instance pool: While adding too many heavily used services to the shared pool can cause performance degradation due to instance contention, it does not explain the rapid consumption of disk space.
C. Federating the additional ArcGIS Server site: Federation is an administrative configuration that links an ArcGIS Server site with a portal. This process itself does not inherently cause service performance issues or fill up disk space in the manner described.
D. Restarting ArcGIS Server: Restarting the server is a common troubleshooting step that typically resolves performance issues by clearing memory and terminating errant processes. It is not a cause of ongoing slow performance or disk space consumption.

1. Esri ArcGIS Enterprise Documentation

"Specify server log settings": "The Debug and Verbose levels are the most descriptive and will cause the server to write the most messages to the logs. Using these levels for a long period of time can quickly consume a large amount of disk space and slow down the server. They are intended to be used only for short periods of time when you are troubleshooting an application."

Source: ArcGIS Enterprise 11.0 Documentation

ArcGIS Server > Administer > Logs > Specify server log settings.

2. Esri ArcGIS Enterprise Documentation

"Configure service instance settings": This document explains how shared instances work. It notes that placing high-traffic services in the shared pool can cause requests to be queued

increasing response times. However

it makes no mention of this action consuming disk space

which is a key symptom in the question.

Source: ArcGIS Enterprise 11.0 Documentation

ArcGIS Server > Services > Tuning and configuring services > Configure service instance settings.