Section: ndctl Manual (1)
ndctl-enable-namespace - enable the given namespace(s)
ndctl enable-namespace <namespace> [<options>]
THEORY OF OPERATION
The capacity of an NVDIMM REGION (contiguous span of persistent memory)
is accessed via one or more NAMESPACE devices. REGION is the Linux term
for what ACPI and UEFI call a DIMM-interleave-set, or a
system-physical-address-range that is striped (by the memory controller)
across one or more memory modules.
The UEFI specification defines the NVDIMM Label Protocol as the
combination of label area access methods and a data format for
provisioning one or more NAMESPACE objects from a REGION. Note that
label support is optional and if Linux does not detect the label
capability it will automatically instantiate a "label-less" namespace
per region. Examples of label-less namespaces are the ones created by
the kernel's memmap=ss!nn command line option (see the nvdimm wiki on
kernel.org), or NVDIMMs without a valid namespace index in their label
Label-less namespaces lack many of the features of their label-rich
cousins. For example, their size cannot be modified, or they cannot be
fully destroyed (i.e. the space reclaimed). A destroy operation will
zero any mode-specific metadata. Finally, for create-namespace operations
on label-less namespaces, ndctl bypasses the region capacity availability
checks, and always satisfies the request using the full region capacity.
The only reconfiguration operation supported on a label-less namespace
is changing its mode.
A namespace can be provisioned to operate in one of 4 modes, fsdax,
devdax, sector, and raw. Here are the expected usage models for
fsdax: Filesystem-DAX mode is the default mode of a namespace
when specifying ndctl create-namespace with no options. It creates
a block device (/dev/pmemX[.Y]) that supports the DAX capabilities
of Linux filesystems (xfs and ext4 to date). DAX removes the page
cache from the I/O path and allows mmap(2) to establish direct
mappings to persistent memory media. The DAX capability enables
workloads / working-sets that would exceed the capacity of the page
cache to scale up to the capacity of persistent memory. Workloads
that fit in page cache or perform bulk data transfers may not see
benefit from DAX. When in doubt, pick this mode.
devdax: Device-DAX mode enables similar mmap(2) DAX mapping
capabilities as Filesystem-DAX. However, instead of a block-device
that can support a DAX-enabled filesystem, this mode emits a single
character device file (/dev/daxX.Y). Use this mode to assign
persistent memory to a virtual-machine, register persistent memory
for RDMA, or when gigantic mappings are needed.
sector: Use this mode to host legacy filesystems that do
not checksum metadata or applications that are not prepared for torn
sectors after a crash. Expected usage for this mode is for small
boot volumes. This mode is compatible with other operating systems.
raw: Raw mode is effectively just a memory disk that does
not support DAX. Typically this indicates a namespace that was
created by tooling or another operating system that did not know how
to create a Linux fsdax or devdax mode namespace. This mode is
compatible with other operating systems, but again, does not support
A namespaceX.Y device name. The keyword all can be specified to carry out
the operation on every namespace in the system, optionally filtered by region
A regionX device name, or a region id number. Restrict the operation to
the specified region(s). The keyword all can be specified to indicate
the lack of any restriction, however this is the same as not supplying a
--region option at all.
A bus id number, or a provider string (e.g. "ACPI.NFIT"). Restrict the
operation to the specified bus(es). The keyword all can be specified
to indicate the lack of any restriction, however this is the same as
not supplying a --bus option at all.
Emit debug messages for the namespace operation
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