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. 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 Best Practice

12. 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 Best Practice

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 http://www.storagemountain.com Using SANs and NAS now available from O’Reilly & Associates Questions to: curtis@thestoragegroup.com