Appendix – JSON File Format

This section is relevant only for the following cases:

Using legacy mode in which the user prefers to not use the recommended SNAP commands, but to use the JSON file format
NVMe-RDMA full offload mode in which the configuration is only possible with the JSON file format

The configuration parameters are divided into two categories: Controller and backends.

Configuration File Examples

Legacy Mode

Note

For the non-full offload mode, it is recommended to use the SNAP RPC commands (described in .SNAP Commands v3.5.0) and not the legacy mode of the JSON file format described in this section.

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            {
  "ctrl": {
    "func_num": 0,
    "rdma_device": "mlx5_2",
    "sqes": 0x6,
    "cqes": 0x4,
    "cq_period": 3,
    "cq_max_count": 6,
    "nr_io_queues": 32,
    "mn": "Mellanox BlueField NVMe SNAP Controller",
    "sn": "MNC12",
    "mdts": 4,
    "oncs": 0,
    "offload": false,
    "max_namespaces": 1024,
    "quirks": 0x0,
    "version": "1.3.0"
  },
  "backends": [
    {
      "type": "spdk_bdev",
      "paths": [
        {
        }
      ]
    }
  ]
}

NVMe-RDMA Full Offload Mode

Note

For NVMe-RDMA full offload mode, users can only use the JSON file format (and not the SNAP RPC commands).

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            {
  "ctrl": {
    "func_num": 0,
    "rdma_device": "mlx5_2",
    "sqes": 0x6,
    "cqes": 0x4,
    "cq_period": 3,
    "cq_max_count": 6,
    "nr_io_queues": 32,
    "mn": "Mellanox BlueField NVMe SNAP Controller",
    "sn": "MNC12",
    "mdts": 4,
    "oncs": 0,
    "offload": true,
    "max_namespaces": 1024,
    "quirks": 0x0
    "version": "1.3.0"
  },
  "backends": [
    {
      "type": "nvmf_rdma",
      "name": "testsubsystem",
      "paths": [
        {
          "addr": "1.1.1.1",
          "port": 4420,
          "ka_timeout_ms": 15000,
          "hostnqn": "r-nvmx03"
        }
      ]
    }
  ]
}

Configuration Parameters

Controller Parameters

Parameters in SNAP JSON configuration file. Default file is located in /etc/mlnx_snap/mlnx_snap.json.

Parameter	Description	Legal Values	Default
rpc_server	Describes the RPC server socket for passing through RPC commands. Relevant only when using vendor-specific RPC commands from host.	Any	""
offload	Enable full-offload mode	true/false	false
nr_io_queues	Maximum number of I/O queues. Note The actual number of queues is limited by number of queues supported by FW.	≥ 0	32
mn	Model number	String (up to 40 chars)	"MLX NVMe Ctrl"
sn	Serial number	String (up to 20 chars)	"MNC12"
nn	Number of namespaces (NN) indicates the maximum value of a valid NSID for the NVM subsystem. If the `mnan` field is cleared to `0h`, then this field also indicates the maximum number of namespaces supported by the NVM subsystem.	0-0xFFFFFFFE	0xFFFFFFFE
mnan	Maximum number of allowed namespaces (MNAN) supported by the NVM subsystem	1-0xFFFFFFFE	1024
mdts	Max data transfer size. This value is in units of the minimum memory page size (CAP.MPSMIN) and is reported as a power of two (2ⁿ). A value of 0h indicates that there is no maximum data transfer size.	1-6	4
quirks	Bitmask for enabling specific NVMe driver quirks in order to work with non-NVMe spec compliant drivers. Bit 0 – send namespace change async events even if driver does not explicitly request them via the SET_FTRS command Note Enable this if the NVMe driver knows to handle namespace change but does not use SET_FTRS. CentOS 7.5 inbox driver does this. Bit 1 – send new namespace change events even if previous ones are not yet cleared by the driver Note CentOS 7.5 inbox driver requires this. Bit 2 – force Number of Namespaces (NN) on Identify controller to dynamically track and indicate both the maximum value of a valid NSID and the maximum number of namespaces supported by the NVM controller. There is no limitation on namespaces NSIDs on controller level. Bit 3 – force OACS to enable namespace management bit Note VMWare driver requires this bit to be set.	0x0-0x3	0x0
max_namespaces	Limit number of available namespaces	Any	1024

Backend Parameters

Theses parameters are used to define the backend server.

Note

Even though a list of backends can be configured, currently only a single backend is supported.

Parameter	Description	Legal Values	Default
type	Backend type: "memdisk" – RAM based local storage "nvmf_rdma" – NVMe-oF over RDMA remote storage "posix_io" – file-based storage "spdk_bdev" – SPDK block devices	nvmf_rdma, spdk_bdev	"spdk_bdev"
name	Depends on backend type: "nvmf_rdma" – remote subsystem name "memdisk"/”spdk_bdev” – unused "posix_io" – backend filename	Any	Null
size_mb	Represents the desired size (in MB) of the opened backend. Relevant only for memdisk/posix_io backends.	Any	Unused
block_order	Represents the desired block size (in logarithmic scale) of the opened backend. Relevant only for memdisk/posix_io backends.	9, 12	Unused

Path Section

This section is relevant only if backend type is set to "nvmf_rdma". For each backend, a list of paths can be specified using the following parameters:

Parameter	Description	Legal Values	Default
addr	Target IPv4 address	String in x.x.x.x format	"192.168.101.2"
port	Target port number	1024-65534	4420
ka_timeout_ms	Keepalive timeout in msec	>0	15000
Nqn	Host NQN	String up to 223-char long	"nqn.2014-08.org.nvmexpress:uuid:11111111-2222-3333-4444-555555555555"

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