When deploying an ArcGIS Server site, you must choose an optimal location to store your site's configuration store and server directories. When choosing a file storage device (NAS/SAN) for this purpose, immediate consistency and performance are essential characteristics to consider for the device. For more information about the configuration store and server directories, see the topics About server directories and About the configuration store.
Immediate consistency
Choose a storage device that enables files to be read immediately from any node in your site once an operation and corresponding write has completed. This distinction disqualifies many types of distributed file systems such as GFS or GlusterFS (Linux).
Performance
Choose a storage device that performs well while incurring volumes of small, random input/output (I/O.) Consider that read and write performance can greatly fluctuate depending on the characteristics of the I/O. This is an important distinction as ArcGIS Server and Portal for ArcGIS operations (interactions with the configuration store, cached bundle tiles, etc.) follow this pattern.
Often this means that a device that has been optimized for large sequential reads and writes (as often occurs with imagery and video) is unsuitable for use with ArcGIS for Server components.
If your implemented file storage mechanism does not handle small, random I/O well, you may experience significantly increased response times or even failures, especially for administrative operations applied in your site.