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HIGH-PERFORMANCE COMPUTING2. The location of files and directories within particular segmentsin the file space is independent of their respective and relativelocations in the namespace. Thus, as shown in Figure 3, adirectory can be located on one segment while the files containedin that directory are spread over other segments. Theselection of segments for placement of files and directoriesoccurs dynamically at the time of file/directory creation asdetermined by an allocation policy. The allocation policy is setby the system administrator in accordance with the anticipatedaccess patterns and specific criteria relevant to the installation(performance, manageability, and so forth).3. Individual files can also be distributed across multiple segments,in cases where very high throughput is desired from asingle file and access patterns are regular and predictable.4. Segment servers are assigned responsibility for managementof individual segments of the file system. Eachsegment is assigned to a single segment server and eachserver can “own” multiple segments, as shown by the colorcoding in Figure 3. Segment ownership can be migratedfrom one server to another while the file system is activelyin use. To meet growing performance needs, additionalservers can be added to the system dynamically withoutadding more capacity by distributing the ownership ofexisting segments for proper load balancing and utilizationof all servers. Conversely, additional capacity can beadded to the file systemwhile in active use withoutadding more servers—ownership of the additionalsegments is distributedamong existing servers.Servers can be configuredwith failover protection,with other servers beingdesignated as standby serversthat automatically takecontrol of a server’s segmentsif a failure occurs.5. Clients run the applicationsthat use the fileSeveral factors should beconsidered when designinga high-performance I/Osubsystem: servers used asI/O nodes, storage technology,file systems, interconnects,and application behavior.system (applications also can run on the segment servers).Clients can access the file system either as a locallymounted cluster file system using the IBRIX driver or usingstandard network attached storage (NAS) protocols such asNFS and Common Internet File System (CIFS).6. Use of the IBRIX driver on the client has significant advantagesover the NAS approach—specifically, the IBRIX driveris aware of the segmented architecture of the file system and,based on the file/directory being accessed, can route requestsFileFile1File2FolderNAS3directly to the correct segment server, yielding balancedresource utilization and high performance.7. When using NAS protocols such as NFS and CIFS, a clientmust mount the file system from one (or more) of the segmentservers. All requests are sent to the mounting serverthat performs the required routing. NAS protocols offer thebenefits of multiplatform support and low administrationcost for the client software, because the client drivers forthese protocols are generally available with the base operatingsystem.8. Segment servers (and clients using the IBRIX driver) areSAN-friendly. A request at a segment server could be for afile on a segment that is either owned by the server, ownedby another server but accessible by this server over theSAN, or owned by another server and not accessible bythis server over the SAN. In the second scenario, the serverobtains the relevant metadata from the owning serverand performs the I/O directly over the SAN. In the thirdscenario, the I/O is performed through the owning serverover the IP network.The segmented architecture is also the basis for fault resilience—loss of access to one or more segments does not render the entirenamespace inaccessible. Individual segments can thus be takenoffline temporarily for maintenance operations and then returnedto the file system.247File18SANMetadataFigure 3. IBRIX segmented file system architectureFile216IP5ClusterSingle namespace130POWER SOLUTIONS Reprinted from Dell Power Solutions, February 2005. Copyright © 2005 Dell Inc. All rights reserved. February 2005