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Version: 3024.10

Performance Tuning Parameters

This section outlines the parameters available for tuning the performance of Fusion SMB. While some parameters have a direct and predictable impact on system performance, others may require experimentation to achieve best results. Additionally, certain parameters may affect system stability, client application's behavior, or other operational aspects. Therefore, any modifications to these settings in production environments should only be made with careful consideration and after thorough testing.

warning

Windows 11 24H2 was officially released on October 1, 2024 and requires signing by default. This may negatively impact performance which is expected and is not Fusion SMB specific behavior. If you need performance over security, simply disable SMB signing requirement on Windows clients. Please see: https://learn.microsoft.com/en-us/windows-server/storage/file-server/smb-signing?tabs=group-policy#disable-smb-signing

System Resources​

This section covers parameters related to system resources, such as the number of open files, concurrent network connections, and active threads in the Fusion SMB process, all of which impact RAM usage.

Network Connections​

Maximum Number of Client Connections​

To increase or decrease the maximum number of client connections, set the connections_max parameter:

Global Parameter Maximum Number of Client Connections

Value Type: integer

Value Format: <connections>
<connections> specifies the maximum number of concurrent client connections allowed to the server. Once the limit is reached, new connections will be rejected. A value of 0 allows for an unlimited number of connections, constrained only by the available system resources.

Default Value: 1024

important

The connections_max parameter in conjunction with the open_files_max parameter, controls the maximum number of open file descriptors Fusion SMB can consume. It is critical to keep the combined total of these two parameters within the system's limit. Misconfiguration may result in the server process crashing.

Maximum Number of Sessions​

To configure the maximum number of client sessions, use the sessions_max parameter:

Global Parameter Configuring the Maximum Number of Sessions

Value Type: integer

Value Format: <sessions>
<sessions> specifies the maximum number of client sessions that can be active on the server at any given time. A value of 0 indicates an unlimited number of sessions.

Default Value: 0.

Multichannel​

Fusion SMB supports multichannel connections for client sessions. For more information see Multichannel.

File Descriptors​

The following parameters control the number of file descriptors consumed by Fusion SMB.

If clients encounter errors when attempting to open files (e.g., STATUS_TOO_MANY_OPENED_FILES on Windows, or ENFILE or EMFILE on Linux/macOS), consider increasing the values of these parameters for raising the system's limit on open files.

Maximum Number of Open Files​

To set the maximum number of open files, adjust the open_files_max parameter:

Global Parameter Maximum Number of Open Files

Value Type: integer

Value Format: <files>
<files> specifies the number of files that can be kept open simultaneously by the server across all client sessions. The minimum value is 1024. A value of 0 indicates that the server will use the system's default value (i.e., the value in /proc/sys/fs/nr_open).

Default Value: 8192

warning

Setting this parameter to a high value on devices with limited RAM may cause significant memory fragmentation, potentially triggering the Out of Memory (OOM) killer.

important

The connections_max parameter in conjunction with the open_files_max parameter, controls the maximum number of open file descriptors that Fusion SMB can consume. It is critical to keep the sum of these parameters below the system's limit. Misconfiguration may result in the server process crashing.

Maximum Number of Open Files per Session​

To set the maximum number of open files per session, adjust the sess_open_files_max parameter:

Global Parameter Maximum Number of Open Files per Session

Value Type: integer

Value Format: <sessions>
The maximum number of open files per session. 0 indicates that the maximum number of open files is unlimited.

Default Value: 1024

important

The sess_open_files_max parameter must be set to a value lower than the value of open-files-max. If it is set to a higher value, a warning will be displayed, and the parameter will automatically revert to its default value of 1024.

Network Threads​

To set the maximum number of network threads, use the transport_rx_threads and transport_tx_threads parameters:

Global Parameter Number of Receive Threads

Value Type: integer

Value Format: <threads>
<threads> specifies the number of transport threads used for receiving data from clients. A value of 0 indicates that the data from packets will be read in the context of the kernel's io_mux threads.

Default Value: 0

Global Parameter Number of Transmit Threads

Value Type: integer

Value Format: <threads>
<threads> specifies the number of transport threads used for sending data to clients.

Default Value: 1

VFS Behavior​

The Virtual File System (VFS) layer in Linux manages file access for all applications, including Fusion SMB. Tuning the interaction between Fusion SMB and VFS can greatly enhance system performance.

VFS Data and Metadata Threads​

Global VFS Thread Pool​

The global VFS thread pool controls the number of threads used to handle data and metadata operations for shares without a dedicated VFS thread pool.

To set the global VFS thread pool, adjust the vfs_data_threads and vfs_metadata_threads parameters:

Global Parameter Number of Metadata Threads
Potentially Overridden by Share Parameter: vfs_metadata_threads

Value Type: integer

Value Format: <threads>
<threads> specifies the number of threads for VFS metadata operations in the global pool (i.e., shared between all shares without a dedicated pool). If set to 0, metadata operations will share the same thread pool as data operations, as specified in the vfs_data_threads parameter.

Default Value: 1

Global Parameter Number of Data Threads
Potentially Overridden by Share Parameter: vfs_data_threads

Value Type: integer

Value Format: <threads>
<threads> specifies the number of threads for VFS data operations in the global pool (shared across all shares without a dedicated pool). If set to 0, data operations will use the same thread pool as metadata operations, as specified by the vfs_metadata_threads parameter.

Default Value: 1

important

It is strongly recommended not to leave vfs_data_threads at the default value of 1. Adjust it to a higher value based on workload requirements.

Additionally, experimentation is advised to determine the optimal values for vfs_data_threads and vfs_metadata_threads for your workload.

Per-Share VFS Thread Pool​

To optimize performance based on each share's specific usage patterns and requirements, you can configure a dedicated VFS thread pool for individual shares:

Share Parameter Number of Data Threads
Potentially Overrides Global Parameter: vfs_data_threads

Value Type: integer

Value Format: <threads>
<threads> specifies the number of threads for VFS data operations in the share's pool. If set to 0:

  • If the share's vfs_metadata_threads is not set to 0, VFS operations will be executed on the share's data thread pool.
  • If the share's vfs_metadata_threads is also set to 0, VFS operations will be executed on the global pool, as specified in the global vfs_data_threads parameter.

Default Value: 1

Share Parameter Number of Metadata Threads
Potentially Overrides Global Parameter: vfs_metadata_threads

Value Type: integer

Value Format: <threads>
<threads> specifies the number of threads for VFS metadata operations in the share's pool. If set to 0:

  • If the share's vfs_data_threads is not set to 0, VFS operations will be executed on the share's data thread pool.
  • If the share's vfs_data_threads is also set to 0, VFS operations will be executed on the global pool, as specified in the global vfs_metadata_threads parameter.

Default Value: 1

important

As with the global VFS thread pool, if a specific share requires a dedicated VFS thread pool, experiment with the number of threads to determine the optimal configuration for your workload.

Zero-Copy​

Zero-copy enhances data transfer performance by minimizing the number of memory copies and system calls. Fusion SMB leverages zero-copy on client read operations by retrieving data from the file system page cache and uses zero-copy to send it directly to the network socket buffer.

important

Regardless of the setting, zero-copy is disabled for all SMB messages that are compound, signed, or encrypted.

The impact of zero-copy on performance varies depending on the workload and underlying storage. It is recommended to evaluate and test this setting within the context of your specific workload.

Toggling Per-Share Zero-Copy Behavior​

To control the zero-copy behavior on a per-share basis by setting the vfs_zerocopy_write and vfs_zerocopy_read parameters in the share configuration:

Share Parameter Toggling Zero-Copy for Read Operations

Value Type: boolean

Value Format: true|false

  • true: Enables zero-copy for read operations on the share.
  • false: Disables zero-copy for read operations on the share.

Default Value: false

Synchronous I/O and Forced Buffering​

To force Fusion SMB to perform synchronous I/O, or to force buffering of write operations into the page cache, regardless of the client's request, adjust the vfs parameter on a per-share basis:

Share Parameter Toggling Synchronous I/O and Forced Buffering

Value Type: string

Value Format: <type>:<option>[,<option>,...]

  • <type> specifies the type of the VFS module to use. Currently, the supported options are:
    • libc: the default VFS module for Linux.
    • module:name=gpfs,path=path/to/tsmb_vfs_gpfs.so: A custom VFS layer for IBM Spectrum® Scale (GPFS). Supports native ACL and Windows extended attribute mapping.
  • <option> can be set to one of the following:
    • force_sync: opens each file with the O_SYNC flag to ensure that all data is written to disk before returning from a write operation. This option is useful for applications requiring strong durability guarantees, but it degrades performance. This option is required for clusters in active-passive mode.
    • nodirect: ignores client requests for direct I/O, bypassing the OS's page cache. This applies to FILE_NO_IMMEDIATE_BUFFERING on Windows, O_DIRECT on Linux, and F_NOCACHE on macOS. This option is likely to improve performance, but could disregard the client application's expectations, potentially resulting in undefined behavior. Use with caution.
    • lock: enables the propagation of byte-range locks to the underlying file system, allowing interoperability with other applications (such as NFS servers) that depend on byte-range locks. Note that this option may degrade performance.
    • nosharemodes: disables GPFS share modes when GPFS VFS module is in use. This option is useful if GPFS share modes cause file access issues. This must always be set when using GPFS.

Default Value: none (libc is configured to not use O_SYNC and to respect client's requests for direct I/O).

Examples:

  • libc:force_sync,nodirect,lock forces Fusion SMB to open all files with the O_SYNC flag, to ignore client's requests for direct I/O, and enables the propogation of byte-range locks to the file system.
  • module:name=gpfs,path=path/to/tsmb_vfs_gpfs.so,nosharemodes enables the IBM Spectrum® Scale (GPFS) VFS module, and disables share modes.

File Space Preallocation​

For workloads that benefit from preallocated file space, you can configure Fusion SMB to preallocate space on the underlying storage using the fallocate() system call.

To enable preallocations on a per-share basis, set the vfs_fallocate_min and vfs_fallocate_max parameters on a share. These parameters define the file size range for which space should be preallocated.

Share Parameter Minimum Size of Preallocated Space

Value Type: integer

Value Format: <bytes>
<bytes> specifies the minimum size of a file that will be allocated using fallocate.

Default Value: 0

Share Parameter Maximum Size of Preallocated Space

Value Type: integer

Value Format: <bytes>
<bytes> specifies the maximum size of a file that will be allocated using fallocate.

Default Value: 0

SMB Behavior​

The following parameters can impact the performance of Fusion SMB by adjusting its behavior within the context of SMB protocol.

Maximum Number of Shares​

To limit the number of shares that can be created, set the shares_max parameter:

Global Parameter Maximum Number of Shares

Value Type: integer

Value Format: <shares>
Specifies the maximum number of shares that can be configured on the server, including both administrative and user shares.

Default Value: 1048576

Case Insensitivity​

In Windows environments, file operations are case-insensitive by default, meaning the file system does not differentiate between uppercase and lowercase characters in file or directory names. For example, MyFile.txt is treated the same as myfile.txt.

However, on Linux–where Fusion SMB operates–file operations are inherently case-sensitive. Hence, file operations on Fusion SMB are case-sensitive by default. For use cases that require case-insensitive operations, you can modify this behavior. Case sensitivity can be controlled globally, or overridden on a per-share basis.

When configured to be case-insensitive, Fusion SMB first attempts to rely on the underlying file system's support for case-insensitive file name resolution. However, if not supported by the file system, Fusion SMB will fall back on performing a case-insensitive comparison of the file name against all the files in the directory.

important

Enabling case-insensitivity can introduce a significant overhead, especially on file systems that don't natively support it, or on large datasets and complex directory trees.

To control case insensitivity, set the case_insensitive parameter, both globally and on a per-share basis:

Global Parameter Setting Case Insensitivity Globally
Overridden by Per-Share Parameter: case_insensitive

Value Type: boolean

Value Format: true|false

  • true: Makes file operations case-insensitive by default.
  • false: Leaves file operations case-sensitive by default.

Default Value: false

Share Parameter Setting Case Insensitivity on a Per-Share Basis
Overrides Global Parameter: case_insensitive

Value Type: boolean

Value Format: true|false

  • true: Makes file operations on the share case-insensitive.
  • false: Leaves file operations on the share case-sensitive.

Default Value: as set in the global configuration.

Opportunistic Locking​

Opportunistic locks (oplocks) enable a client to cache file data locally, boosting performance by reducing the frequency of message exchanges between the client and server. With an oplock obtained, the client can perform certain operations on the file locally without immediately notifying the server, thereby minimizing network traffic.

If another client attempts to access the same file, the server revokes the oplock, prompting the original client to flush its cached data to the server to maintain data consistency.

Oplocks improve performance in single-client scenarios while ensuring data integrity in multi-client environments.

Global Oplock Behavior​

To control the global oplock behavior, set the oplock parameter:

Global Parameter Global Oplock Behavior
Potentially Overridden by Share Parameter: oplock

Value Type: string

Value Format: <type>
<type> specifies the type of opportunistic lock to be issued:

  • all: Full oplock/lease support.
  • disabled: Disables oplock/lease support. This prevents the server from advertising the SMB2_GLOBAL_CAP_LEASING capability to clients.
  • none: Enables oplock/lease support and advertises the SMB2_GLOBAL_CAP_LEASING capability to clients. However, Fusion SMB server only grants NONE oplock/lease regardless of the value of RequestedOplockLevel.
  • exclusive: Similar to all, however only one oplock can be granted on a file at a time. Multiple clients can access a file, as long as there are no oplocks on it, or all clients have the same lease key.

Default Value: all

Controlling the Type of Oplocks Issued for a Share​

You can configure the type of opportunistic locks (oplocks) issued by Fusion SMB, restricting them to Level 2 (read-only) oplocks, or disabling them entirely.

Restricting oplocks to read-only can be useful for read-heavy workloads, as it improves performance by minimizing the need for oplock revocations.

Share Parameter Controlling the Type of Oplocks Issued for a Share
Potentially Overrides Global Parameter: oplock
Ignored when global parameter oplock is set to disabled

Value Type: string

Value Format: <type>
<type> specifies the type of opportunistic lock to be issued:

  • none: Enables oplock/lease support and advertises the SMB2_GLOBAL_CAP_LEASING capability to clients. However, Fusion SMB server only grants NONE oplock/lease regardless of the value of RequestedOplockLevel.
  • read: Read-only oplock/lease support. This may be used to increase performance when the workload mostly consists of read operations.
  • all: Full oplock/lease support.

Default Value: all

SMB2 Credits​

To control the number of credits that are issued to clients, set the smb2_credits_max parameter:

Global Parameter Number of SMB2 Credits

Value Type: integer

Value Format: <credits>
<credits> specifies the maximum amount of credits the server will advertise to clients.

Default Value: 8092

Message Size Limits​

To control the maximum size of SMB messages advertised to clients, set the smb2_read_max, smb2_write_max, and smb2_trans_max parameters:

Global Parameter Maximum Size of SMB Messages for Read Operations

Value Type: integer

Value Format: <bytes>
<bytes> specifies the maximum data size the server can return in a single READ operation to the client. The maximum value is determined by the SMB dialect being used.

Default Value:

  • 65536 for dialect 2.002 and lower
  • 8388608 for dialect 2.1 and higher
Global Parameter Maximum Size of SMB Messages for Write Operations

Value Type: integer

Value Format: <bytes>
Where <bytes> will be used to communicate to the client the maximum data size the server will accept in a single WRITE operation. The maximum value is determined by the SMB dialect being used.

Default Value:

  • 65536 for dialect 2.002 and lower
  • 8388608 for dialect 2.1 and higher
Global Parameter Maximum Size of SMB Messages for Transact Operations

Value Type: integer

Value Format: <bytes>
<bytes> specifies the maximum buffer size that may be used for QUERY, SET, and NOTIFY operations. This value is communicated to the client. The maximum value is determined by the SMB dialect in use.

Default Value:

  • 65536 for dialect 2.002 and lower
  • 8388608 for dialect 2.1 and higher