SAN vs. NAS Shared Storage for Failover Clustering: A Detailed Comparison

What is the simplest solution between a SAN vs a NAS shared storage for a failover cluster?

SAN shared storage or NAS iSCSI shared storage for a failover cluster

There are several elements that make this architecture complex to implement:

• on failover, switching the shared storage requires low level instructions which are storage manufacturer dependent,
• recovery procedure on the file system (FS) must be passed before restarting the application,
• if both file systems on both nodes access the same raw disk at the same time, the full file system will be corrupted,
• to avoid a double access, a quorum disk must be configured.

NAS SMB shared storage or NAS NFS shared storage for a failover cluster

There are several elements that make this architecture simple to implement:

• on failover, switching the shared storage means only remounting the external file system,
• no recovery procedure on the file system must be passed before restarting the application,
• if both nodes access the same shared file system at the same time, the full file system will be not be corrupted,
• however, there is still the possibility of a double execution of the same application corrupting its data in the shared storage when nodes are isolated.

Real-time replication and failover with Eviden SafeKit

There are no such issues with SafeKit because its replication and failover solution does not require a shared storage.

However, if SafeKit must manage a shared storage:

• use a NAS SMB shared storage or a NAS NFS shared storage,
• put in the restart scripts the mount/umount of the external file system,
• configure the SafeKit split brain checker to avoid a double execution of the same application accessing the shared storage when nodes are isolated.

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