Dell PowerFlex Appliance with PowerFlex 4.x Administration Guide

Sync Writes: Synchronous writes enable the storage system to perform immediate synchronous writes for storage operations, regardless of how the SMB protocol performs write operations. Enabling synchronous writes operations allow you to store and access database files (for example, MySQL) on storage system SMB shares. This option guarantees that any write to the share is done synchronously and reduces the chances of data loss or file corruption in various failure scenarios, for example, loss of power. If SMB3 continuous availability (CA) is enabled, all write operations are automatically synced to satisfy the requirements for continuous availability. This option can have a big impact on performance. It is not recommended unless you intend to use Windows file systems to provide storage for database applications.

Oplocks: Opportunistic file locks (oplocks) allow SMB clients to buffer file data locally before sending it to a server. SMB clients can then work with files locally and periodically communicate changes to the storage system rather than having to communicate every operation over the network to the storage system. Unless your application handles critical data or has specific requirements that make this mode or operation unfeasible, leaving the oplocks enabled is recommended.

The following oplocks implementations are supported:

• Level II oplocks: This informs a client that multiple clients are currently accessing a file, but no client has yet modified it. A level II oplock lets the client perform read operations and file-attribute fetches by using cached or read-ahead local information. All other file access requests must be sent to the server.
• Exclusive oplocks (SMB2 only): This informs a client that it is the only client opening the file. An exclusive oplock lets a client perform all file operations by using cached or read-ahead information until it closes the file, at which time the server must be updated with any changes that are made to the state of the file (contents and attributes).
• Batch oplocks: This informs a client that it is the only client opening the file. A batch oplock lets a client perform all file operations by using cached or read-ahead information (including opens and closes). The server can keep a file opened for a client even though the local process on the client machine has closed the file. This mechanism curtails the amount of network traffic by letting clients skip the extraneous close and open requests.

This option only applies to client access over SMB1 since oplocks are always enabled for client access over SMB2 and SMB3. However, disabling this option also invalidates the SMB2.1 file and directory lease feature. Leasing serves the same purpose as oplocks, but provides greater flexibility and enhancements, increasing performance and reducing network utilization.

• Read-caching lease: This allows caching reads and can be shared by multiple clients.
• Write-caching lease: This allows caching writes and is exclusive to only one client.
• Handle-caching lease: This allows caching handles and can be shared by multiple clients.

Notify on write or access: This option enables notifications when a file system is written to or accessed. Applications that run on Windows platforms, and use the Win32 API, can register with the SMB server to be notified of file and directory content changes, such as file creation, modify, or rename. For example, this feature can indicate when a display must be refreshed (Windows Explorer) or when the cache must be refreshed (Microsoft Internet Information Server), without having to constantly poll the SMB server.