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How to Cluster both Servers and Storage

How to Cluster both Servers and Storage. W. Curtis Preston President The Storage Group. What is a Cluster?. Two or more servers that behave like one Purists will say it should be several servers Many “clustering” products have supported only two members of a single cluster Active/passive

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How to Cluster both Servers and Storage

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  1. How to Cluster both Servers and Storage W. Curtis Preston President The Storage Group

  2. What is a Cluster? • Two or more servers that behave like one • Purists will say it should be several servers • Many “clustering” products have supported only two members of a single cluster • Active/passive • Standby resource is not used until failure occurs • Active/active • All resources in cluster share the application load • Failure of one node increases the load on remaining nodes • Node resumes its role if it returns to cluster

  3. Why Cluster? Application Availability • Goal is to ensure that application is always available, even if a cluster member is down • Active/passive: application continues to function if standby server is available • Active/active: application continues to function if at least one member of cluster is available

  4. Why Cluster? Performance and Scalability • The load is distributed across multiple servers • Applications can perform faster than on any single server • Large I/O requests (For example, Web farms) • Large database queries and processing (For example, parallel database) • Applications can scale farther than on any single server • Can increase capacity by adding node to the cluster • Capacity can be added without stopping application

  5. Examples of Clustering • VAX • IBM S/390 • SP/2 • VERITAS Cluster Server • MS Cluster

  6. Shared Storage Clustering • Storing function • Shared SPI (parallel SCSI) • Possibly other bus topology • Filing function • Non-shared file systems • Serving function • Clustering was done here • Clustering application responsible for locking data and time-sharing write access to disk

  7. Independent Storage Clustering • Storing function • Non-shared storage, even in fail over • Filing function • Non-shared file systems • Files and file systems mirrored between nodes using software • Serving function • Clustering still done here • No longer need to time-share write access to disk • Increases availability • Either node can service application via its own mirrored copy of the data

  8. Storage Can be Clustered Too! • To cluster our storage, we need multiple resources acting as one virtual resource • Can push the purposes of clustering to the storage level • Increase the capacity of the storage system by distributing the load • Increase the availability of the application by increasing entire system’s ability to • Sense • Report • Recover

  9. Clustering the Storing Function • Two or more disks, virtual disks, or arrays can be made to appear as one • Functionality provided by • SAN-aware Volume Managers • I/O based mirroring • Intelligent routers • Can fulfill performance, scalability, and availability purposes of clustering • Note: Filing function not clustered

  10. Clustering the Filing Function • Clustering on the backend • Allows multiple machines to access the filesystem as if they were one machine. • Software required on each server that will access filesystem • Several proprietary products available today • DAFS is a future, non-proprietary filesystem that should offer this functionality • Note: Storing function not clustered

  11. Best Practice Clustering Storing and Filing with SAN • Combine a single, clustered, virtual volume with a single, clustered virtual filesystem • Clustering end to end • Load distributed between all available servers, disks, and SAN components • Any server, SAN component, or disk array, is backed up by at least one other

  12. Best Practice Clustering Storing and Filing with NAS • NAS vendors also offer a complete clustered solution • NFS or CIFS already a multiple access filesystem • Also uses clustered storage on backend • Can offer similar levels of availability, performance, and scalability as a SAN-based product, with a proven file system

  13. Future Developments • Distributed filesystems • Existing products should become more mature • New products will drive competition • DAFS • Will bridge the gap between SAN and NAS • iSCSI • Allow for use of traditional network management tools in SAN • Could also use OSPF instead of FSPF

  14. Clustering is a Good Thing • Clustering a system’s serving, filing and storing functions results in a completely clustered, load-balanced, high-available system • There is more than one way to do it! • Fibre Channel SAN • iSCSI SAN • NAS with NFS/CIFS • NAS with DAFS

  15. Learn more… • Directory of vendors offering storage clustering options:http://www.storagemountain.com • Using SANs and NAS now available from O’Reilly & Associates • Questions to:curtis@thestoragegroup.com

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