Red Hat Summit18.6. Creating a device DAX namespace on an NVDIMM
Configure the NVDIMM device that is attached to your system, in device DAX mode to support character storage with direct access capabilities.
To do this, consider the following options:
- Reconfiguring an existing namespace to device DAX mode.
- Creating a new device DAX namespace, if there is space available.
18.6.1. NVDIMM in device direct access mode
Device direct access (device DAX, devdax) provides a means for applications to directly access storage, without the involvement of a file system. The benefit of device DAX is that it provides a guaranteed fault granularity, which can be configured using the --align option of the ndctl utility.
For the Intel 64 and AMD64 architecture, the following fault granularities are supported:
- 4 KiB
- 2 MiB
- 1 GiB
Device DAX nodes support only the following system calls:
-
open() -
close() -
mmap()
You can view the supported alignments of your NVDIMM device using the ndctl list --human --capabilities command. For example, to view it for the region0 device, use the ndctl list --human --capabilities -r region0 command.
The read() and write() system calls are not supported because the device DAX use case is tied to the SNIA Non-Volatile Memory Programming Model.
18.6.2. Reconfiguring an existing NVDIMM namespace to device DAX mode
You can reconfigure an existing Non-Volatile Dual In-line Memory Modules (NVDIMM) namespace to device DAX mode.
Reconfiguring a namespace deletes previously stored data on the namespace.
Prerequisites
-
The
ndctlutility is installed. For more information, see Installing ndctl.
Procedure
List all namespaces on your system:
# ndctl list --namespaces --idle [ { "dev":"namespace1.0", "mode":"raw", "size":34359738368, "uuid":"ac951312-b312-4e76-9f15-6e00c8f2e6f4" "state":"disabled", "numa_node":1 }, { "dev":"namespace0.0", "mode":"raw", "size":38615912448, "uuid":"ff5a0a16-3495-4ce8-b86b-f0e3bd9d1817", "state":"disabled", "numa_node":0 } ]Reconfigure any namespace:
# ndctl create-namespace --force --mode=devdax --reconfig=namespace-ID例18.1 Reconfiguring a namespace as device DAX
The following command reconfigures
namespace0.1for data storage that supports DAX. It is aligned to a 2-MiB fault granularity to ensure that the operating system faults in 2-MiB pages at a time:# ndctl create-namespace --force --mode=devdax --align=2M --reconfig=namespace0.1 { "dev":"namespace0.1", "mode":"devdax", "map":"dev", "size":"35.44 GiB (38.05 GB)", "uuid":"426d6a52-df92-43d2-8cc7-046241d6d761", "daxregion":{ "id":0, "size":"35.44 GiB (38.05 GB)", "align":2097152, "devices":[ { "chardev":"dax0.1", "size":"35.44 GiB (38.05 GB)", "target_node":4, "mode":"devdax" } ] }, "align":2097152 }The namespace is now available at the
/dev/dax0.1path.
Verification
Verify if the existing namespaces on your system is reconfigured:
# ndctl list --namespace namespace0.1 [ { "dev":"namespace0.1", "mode":"devdax", "map":"dev", "size":38048628736, "uuid":"426d6a52-df92-43d2-8cc7-046241d6d761", "chardev":"dax0.1", "align":2097152 } ]
18.6.3. Creating a new NVDIMM namespace in device DAX mode
You can create a new device DAX namespace on a Non-Volatile Dual In-line Memory Modules (NVDIMM) device if there is available space in the region.
Prerequisites
-
The
ndctlutility is installed. For more information, see Installing ndctl. The NVDIMM device supports labels to create multiple namespaces in a region. You can check this using the following command:
# ndctl read-labels nmem0 >/dev/null read 1 nmemThis indicates that it read the label of one NVDIMM device. If the value is
0, it implies that your device does not support labels.
Procedure
List the
pmemregions on your system that have available space. In the following example, space is available in the region1 and region0 regions:# ndctl list --regions [ { "dev":"region1", "size":2156073582592, "align":16777216, "available_size":2117418876928, "max_available_extent":2117418876928, "type":"pmem", "iset_id":-9102197055295954944, "badblock_count":1, "persistence_domain":"memory_controller" }, { "dev":"region0", "size":2156073582592, "align":16777216, "available_size":2143188680704, "max_available_extent":2143188680704, "type":"pmem", "iset_id":736272362787276936, "badblock_count":3, "persistence_domain":"memory_controller" } ]Allocate one or more namespaces on any of the available regions:
# ndctl create-namespace --mode=devdax --region=regionN --size=namespace-sizeFor example, the following command creates a 36-GiB device DAX namespace on
region0. It is aligned to a 2-MiB fault granularity to ensure that the operating system faults in 2-MiB pages at a time:# ndctl create-namespace --mode=devdax --region=region0 --align=2M --size=36G { "dev":"namespace0.2", "mode":"devdax", "map":"dev", "size":"35.44 GiB (38.05 GB)", "uuid":"89d13f41-be6c-425b-9ec7-1e2a239b5303", "daxregion":{ "id":0, "size":"35.44 GiB (38.05 GB)", "align":2097152, "devices":[ { "chardev":"dax0.2", "size":"35.44 GiB (38.05 GB)", "target_node":4, "mode":"devdax" } ] }, "align":2097152 }The namespace is now available as
/dev/dax0.2.
Verification
Verify if the new namespace is created in device DAX mode:
# ndctl list -RN -n namespace0.2 { "regions":[ { "dev":"region0", "size":2156073582592, "align":16777216, "available_size":2065879269376, "max_available_extent":2065879269376, "type":"pmem", "iset_id":736272362787276936, "badblock_count":3, "persistence_domain":"memory_controller", "namespaces":[ { "dev":"namespace0.2", "mode":"devdax", "map":"dev", "size":38048628736, "uuid":"89d13f41-be6c-425b-9ec7-1e2a239b5303", "chardev":"dax0.2", "align":2097152 } ] } ] }
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