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doc: Minor updates to bdev user guide

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Signed-off-by: Monica Kenguva <monica.kenguva@intel.com>
Change-Id: I28047e71535046b898fa14bfb210ec4019614554
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/3465
Community-CI: Mellanox Build Bot
Reviewed-by: Tomasz Zawadzki <tomasz.zawadzki@intel.com>
Reviewed-by: Ben Walker <benjamin.walker@intel.com>
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
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Monica Kenguva 2020-07-20 22:12:10 +00:00 committed by Tomasz Zawadzki
parent b68d89bcc2
commit 802fd5bf41
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@ -1,5 +1,9 @@
# Block Device User Guide {#bdev}
# Target Audience {#bdev_ug_targetaudience}
This user guide is intended for software developers who have knowledge of block storage, storage drivers, issuing JSON-RPC commands and storage services such as RAID, compression, crypto, and others.
# Introduction {#bdev_ug_introduction}
The SPDK block device layer, often simply called *bdev*, is a C library
@ -35,72 +39,12 @@ directly from SPDK application by running `scripts/rpc.py rpc_get_methods`.
Detailed help for each command can be displayed by adding `-h` flag as a
command parameter.
# General Purpose RPCs {#bdev_ug_general_rpcs}
# Configuring Block Device Modules {#bdev_ug_general_rpcs}
## bdev_get_bdevs {#bdev_ug_get_bdevs}
Block devices can be configured using JSON RPCs. A complete list of available RPC commands
with detailed information can be found on the @ref jsonrpc_components_bdev page.
List of currently available block devices including detailed information about
them can be get by using `bdev_get_bdevs` RPC command. User can add optional
parameter `name` to get details about specified by that name bdev.
Example response
~~~
{
"num_blocks": 32768,
"assigned_rate_limits": {
"rw_ios_per_sec": 10000,
"rw_mbytes_per_sec": 20
},
"supported_io_types": {
"reset": true,
"nvme_admin": false,
"unmap": true,
"read": true,
"write_zeroes": true,
"write": true,
"flush": true,
"nvme_io": false
},
"driver_specific": {},
"claimed": false,
"block_size": 4096,
"product_name": "Malloc disk",
"name": "Malloc0"
}
~~~
## bdev_set_qos_limit {#bdev_set_qos_limit}
Users can use the `bdev_set_qos_limit` RPC command to enable, adjust, and disable
rate limits on an existing bdev. Two types of rate limits are supported:
IOPS and bandwidth. The rate limits can be enabled, adjusted, and disabled at any
time for the specified bdev. The bdev name is a required parameter for this
RPC command and at least one of `rw_ios_per_sec` and `rw_mbytes_per_sec` must be
specified. When both rate limits are enabled, the first met limit will
take effect. The value 0 may be specified to disable the corresponding rate
limit. Users can run this command with `-h` or `--help` for more information.
## Histograms {#rpc_bdev_histogram}
The `bdev_enable_histogram` RPC command allows to enable or disable gathering
latency data for specified bdev. Histogram can be downloaded by the user by
calling `bdev_get_histogram` and parsed using scripts/histogram.py script.
Example command
`rpc.py bdev_enable_histogram Nvme0n1 --enable`
The command will enable gathering data for histogram on Nvme0n1 device.
`rpc.py bdev_get_histogram Nvme0n1 | histogram.py`
The command will download gathered histogram data. The script will parse
the data and show table containing IO count for latency ranges.
`rpc.py bdev_enable_histogram Nvme0n1 --disable`
The command will disable histogram on Nvme0n1 device.
# Common Block Device Configuration Examples
# Ceph RBD {#bdev_config_rbd}
@ -378,6 +322,14 @@ please visit [OCF documentation](https://open-cas.github.io/).
Malloc bdevs are ramdisks. Because of its nature they are volatile. They are created from hugepage memory given to SPDK
application.
Example command for creating malloc bdev:
`rpc.py bdev_malloc_create -b Malloc0 64 512`
Example command for removing malloc bdev:
`rpc.py bdev_malloc_delete Malloc0`
# Null {#bdev_config_null}
The SPDK null bdev driver is a dummy block I/O target that discards all writes and returns undefined
@ -460,7 +412,6 @@ User can get list of available lvol stores using `bdev_lvol_get_lvstores` RPC co
parameters available).
Example response
~~~
{
"uuid": "330a6ab2-f468-11e7-983e-001e67edf35d",