With a cluster file system, each client workstation requires proprietary Installable File System (IFS) software and special hardware adaptors that support Fibre Channel or iSCSI protocols. Installation and upgrades of the IFS software requires planned downtime. Users also suffer from limited operating system/version support for IFS software and long lead times for IFS software certification on new operating systems/versions.
Without IFS software or a special hardware adaptor, a client workstation can only access the cluster file system storage via a NAS gateway, which translates between CIFS and the proprietary file system protocol. A NAS gateway incurs additional costs and introduces single point of failure (SPOF), access latency, and performance bottlenecks. Fault resiliency and performance are also limited by the metadata server as it handles all the file system and data replication processing for the entire cluster. Redundant pairing of metadata servers alleviates the SPOF issue, but exacerbates the performance bottleneck due to constant metadata mirroring.
A cluster file system relies on mirroring (also known as replication) for data protection, an overhead that consumes at least 50% of the total storage capacity. To increase storage capacity a user’s only option is to add entire storage arrays. Compared to storage expansions, a storage array incurs greater expense due to its various hardware components required for networking, Fibre Channel/iSCSI processing, and RAID processing. Metadata servers, NAS gateways, and client host adaptors also contribute significantly to the hardware and software acquisition costs.
To manage a cluster file system, the customer has to manage the storage arrays for LUN and RAID configurations, manage the metadata servers for redundancy and metadata mirroring, manage the client workstations for IFS software install and upgrades, manage the NAS gateways for CIFS access, and manage three different networks – client to metadata server network, metadata server to metadata server network, and client to storage array network. The cost of deploying and managing such a complex system often far exceeds the acquisition cost of the
hardware and software.