NAME

       ndctl-enable-namespace - enable the given namespace(s)

SYNOPSIS

       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 area.

           Note
           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 these modes:

       •   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 DAX operation.

OPTIONS

       <namespace>
           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 (see
           --region=option)

       -r, --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.

       -b, --bus=
           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.

       -v, --verbose
           Emit debug messages for the namespace operation

COPYRIGHT

       Copyright (c) 2016 - 2019, Intel Corporation. License GPLv2: GNU GPL version 2
       http://gnu.org/licenses/gpl.html. This is free software: you are free to change and
       redistribute it. There is NO WARRANTY, to the extent permitted by law.

SEE ALSO

       ndctl-disable-namespace(1)