[PATCH 2/2] dm-ioband: I/O bandwidth controller v1.0.0: Document

[Ryo Tsuruta]

Here is the document of dm-ioband.

Based on 2.6.26-rc2-mm1
Signed-off-by: Ryo Tsuruta <ryov@xxxxxxxxxxxxx>
Signed-off-by: Hirokazu Takahashi <taka@xxxxxxxxxxxxx>

diff -uprN linux-2.6.26-rc2-mm1.orig/Documentation/device-mapper/ioband.txt linux-2.6.26-rc2-mm1/Documentation/device-mapper/ioband.txt
--- linux-2.6.26-rc2-mm1.orig/Documentation/device-mapper/ioband.txt	1970-01-01 09:00:00.000000000 +0900
+++ linux-2.6.26-rc2-mm1/Documentation/device-mapper/ioband.txt	2008-05-19 14:22:37.000000000 +0900
@@ -0,0 +1,899 @@
+                     Block I/O bandwidth control: dm-ioband
+
+            -------------------------------------------------------
+
+   Table of Contents
+
+   [1]What's dm-ioband all about?
+
+   [2]Differences from the CFQ I/O scheduler
+
+   [3]How dm-ioband works.
+
+   [4]Setup and Installation
+
+   [5]Getting started
+
+   [6]Command Reference
+
+   [7]Examples
+
+What's dm-ioband all about?
+
+     dm-ioband is an I/O bandwidth controller implemented as a device-mapper
+   driver. Several jobs using the same physical device have to share the
+   bandwidth of the device. dm-ioband gives bandwidth to each job according
+   to its weight, which each job can set its own value to.
+
+     At this time, a job is a group of processes with the same pid or pgrp or
+   uid. There is also a plan to make it support cgroup. A job can also be a
+   virtual machine such as KVM or Xen.
+
+     +------+ +------+ +------+   +------+ +------+ +------+
+     |cgroup| |cgroup| | the  |   | pid  | | pid  | | the  |  jobs
+     |  A   | |  B   | |others|   |  X   | |  Y   | |others|
+     +--|---+ +--|---+ +--|---+   +--|---+ +--|---+ +--|---+
+     +--V----+---V---+----V---+   +--V----+---V---+----V---+
+     | group | group | default|   | group | group | default|  ioband groups
+     |       |       |  group |   |       |       |  group |
+     +-------+-------+--------+   +-------+-------+--------+
+     |        ioband1         |   |       ioband2          |  ioband devices
+     +-----------|------------+   +-----------|------------+
+     +-----------V--------------+-------------V------------+
+     |                          |                          |
+     |          sdb1            |           sdb2           |  physical devices
+     +--------------------------+--------------------------+
+
+
+   --------------------------------------------------------------------------
+
+Differences from the CFQ I/O scheduler
+
+     Dm-ioband is flexible to configure the bandwidth settings.
+
+     Dm-ioband can work with any type of I/O scheduler such as the NOOP
+   scheduler, which is often chosen for high-end storages, since it is
+   implemented outside the I/O scheduling layer. It allows both of partition
+   based bandwidth control and job --- a group of processes --- based
+   control. In addition, it can set different configuration on each physical
+   device to control its bandwidth.
+
+     Meanwhile the current implementation of the CFQ scheduler has 8 IO
+   priority levels and all jobs whose processes have the same IO priority
+   share the bandwidth assigned to this level between them. And IO priority
+   is an attribute of a process so that it equally effects to all block
+   devices.
+
+   --------------------------------------------------------------------------
+
+How dm-ioband works.
+
+     Every ioband device has one ioband group, which by default is called the
+   default group.
+
+     Ioband devices can also have extra ioband groups in them. Each ioband
+   group has a job to support and a weight. Proportional to the weight,
+   dm-ioband gives tokens to the group.
+
+     A group passes on I/O requests that its job issues to the underlying
+   layer so long as it has tokens left, while requests are blocked if there
+   aren't any tokens left in the group. Tokens are refilled once all of
+   groups that have requests on a given physical device use up their tokens.
+
+     There are two policies for token consumption. One is that a token is
+   consumed for each I/O request. The other is that a token is consumed for
+   each I/O sector, for example, one I/O request which consists of
+   4Kbytes(512bytes * 8 sectors) read consumes 8 tokens. A user can choose
+   either policy.
+
+     With this approach, a job running on an ioband group with large weight
+   is guaranteed a wide I/O bandwidth.
+
+   --------------------------------------------------------------------------
+
+Setup and Installation
+
+     Build a kernel with these options enabled:
+
+     CONFIG_MD
+     CONFIG_BLK_DEV_DM
+     CONFIG_DM_IOBAND
+
+
+     If compiled as module, use modprobe to load dm-ioband.
+
+     # make modules
+     # make modules_install
+     # depmod -a
+     # modprobe dm-ioband
+
+
+     "dmsetup targets" command shows all available device-mapper targets.
+   "ioband" is displayed if dm-ioband has been loaded.
+
+     # dmsetup targets
+     ioband           v1.0.0
+
+
+   --------------------------------------------------------------------------
+
+Getting started
+
+     The following is a brief description how to control the I/O bandwidth of
+   disks. In this description, we'll take one disk with two partitions as an
+   example target.
+
+   --------------------------------------------------------------------------
+
+  Create and map ioband devices
+
+     Create two ioband devices "ioband1" and "ioband2". "ioband1" is mapped
+   to "/dev/sda1" and has a weight of 40. "ioband2" is mapped to "/dev/sda2"
+   and has a weight of 10. "ioband1" can use 80% --- 40/(40+10)*100 --- of
+   the bandwidth of the physical disk "/dev/sda" while "ioband2" can use 20%.
+
+    # echo "0 $(blockdev --getsize /dev/sda1) ioband /dev/sda1 1 0 0 none" \
+        "weight 0 :40" | dmsetup create ioband1
+    # echo "0 $(blockdev --getsize /dev/sda2) ioband /dev/sda2 1 0 0 none" \
+        "weight 0 :10" | dmsetup create ioband2
+
+
+     If the commands are successful then the device files
+   "/dev/mapper/ioband1" and "/dev/mapper/ioband2" will have been created.
+
+   --------------------------------------------------------------------------
+
+  Additional bandwidth control
+
+     In this example two extra ioband groups are created on "ioband1". The
+   first group consists of all the processes with user-id 1000 and the second
+   group consists of all the processes with user-id 2000. Their weights are
+   30 and 20 respectively.
+
+    # dmsetup message ioband1 0 type user
+    # dmsetup message ioband1 0 attach 1000
+    # dmsetup message ioband1 0 attach 2000
+    # dmsetup message ioband1 0 weight 1000:30
+    # dmsetup message ioband1 0 weight 2000:20
+
+
+     Now the processes in the user-id 1000 group can use 30% ---
+   30/(30+20+40+10)*100 --- of the bandwidth of the physical disk.
+
+   Table 1. Weight assignments
+
+   +----------------------------------------------------------------+
+   | ioband device |          ioband group          | ioband weight |
+   |---------------+--------------------------------+---------------|
+   | ioband1       | user id 1000                   | 30            |
+   |---------------+--------------------------------+---------------|
+   | ioband1       | user id 2000                   | 20            |
+   |---------------+--------------------------------+---------------|
+   | ioband1       | default group(the other users) | 40            |
+   |---------------+--------------------------------+---------------|
+   | ioband2       | default group                  | 10            |
+   +----------------------------------------------------------------+
+
+   --------------------------------------------------------------------------
+
+  Remove the ioband devices
+
+     Remove the ioband devices when no longer used.
+
+     # dmsetup remove ioband1
+     # dmsetup remove ioband2
+
+
+   --------------------------------------------------------------------------
+
+Command Reference
+
+  Create an ioband device
+
+   SYNOPSIS
+
+           dmsetup create IOBAND_DEVICE
+
+   DESCRIPTION
+
+             Create an ioband device with the given name IOBAND_DEVICE.
+           Generally, dmsetup reads a table from standard input. Each line of
+           the table specifies a single target and is of the form:
+
+             start_sector num_sectors "ioband" device_file ioband_device_id \
+                 io_throttle io_limit ioband_group_type policy token_base \
+                 :weight [ioband_group_id:weight...]
+
+
+                start_sector, num_sectors
+
+                          The sector range of the underlying device where
+                        dm-ioband maps.
+
+                ioband
+
+                          Specify the string "ioband" as a target type.
+
+                device_file
+
+                          Underlying device name.
+
+                ioband_device_id
+
+                          The ID number for an ioband device. The same ID
+                        must be set among the ioband devices that share the
+                        same bandwidth, which means they work on the same
+                        physical disk.
+
+                io_throttle
+
+                          Dm-ioband starts to control the bandwidth when the
+                        number of BIOs in progress exceeds this value. If 0
+                        is specified, dm-ioband uses the default value.
+
+                io_limit
+
+                          Dm-ioband blocks all I/O requests for the
+                        IOBAND_DEVICE when the number of BIOs in progress
+                        exceeds this value. If 0 is specified, dm-ioband uses
+                        the default value.
+
+                ioband_group_type
+
+                          Specify how to evaluate the ioband group ID. The
+                        type must be one of "none", "user", "gid", "pid" or
+                        "pgrp." Specify "none" if you don't need any ioband
+                        groups other than the default ioband group.
+
+                policy
+
+                          Specify bandwidth control policy. A user can choose
+                        either policy "weight" or "weight-iosize."
+
+                             weight
+
+                                       This policy controls bandwidth
+                                     according to the proportional to the
+                                     weight of each ioband group based on the
+                                     number of I/O requests.
+
+                             weight-iosize
+
+                                       This policy controls bandwidth
+                                     according to the proportional to the
+                                     weight of each ioband group based on the
+                                     number of I/O sectors.
+
+                token_base
+
+                          The number of tokens which specified by token_base
+                        will be distributed to all ioband groups according to
+                        the proportional to the weight of each ioband group.
+                        If 0 is specified, dm-ioband uses the default value.
+
+                ioband_group_id:weight
+
+                          Set the weight of the ioband group specified by
+                        ioband_group_id. If ioband_group_id is omitted, the
+                        weight is assigned to the default ioband group.
+
+   EXAMPLE
+
+             Create an ioband device with the following parameters:
+
+              *   Starting sector = "0"
+
+              *   The number of sectors = "$(blockdev --getsize /dev/sda1)"
+
+              *   Target type = "ioband"
+
+              *   Underlying device name = "/dev/sda1"
+
+              *   Ioband device ID = "128"
+
+              *   I/O throttle = "10"
+
+              *   I/O limit = "400"
+
+              *   Ioband group type = "user"
+
+              *   Bandwidth control policy = "weight"
+
+              *   Token base = "2048"
+
+              *   Weight for the default ioband group = "100"
+
+              *   Weight for the ioband group 1000 = "80"
+
+              *   Weight for the ioband group 2000 = "20"
+
+              *   Ioband device name = "ioband1"
+
+             # echo "0 $(blockdev --getsize /dev/sda1) ioband" \
+               "/dev/sda1 128 10 400 user weight 2048 :100 1000:80 2000:20" \
+               | dmsetup create ioband1
+
+
+             Create two device groups (ID=1,2). The bandwidths of these
+           device groups will be individually controlled.
+
+             # echo "0 $(blockdev --getsize /dev/sda1) ioband /dev/sda1 1" \
+               "0 0 none weight 0 :80" | dmsetup create ioband1
+             # echo "0 $(blockdev --getsize /dev/sda2) ioband /dev/sda2 1" \
+               "0 0 none weight 0 :20" | dmsetup create ioband2
+             # echo "0 $(blockdev --getsize /dev/sdb3) ioband /dev/sdb3 2" \
+               "0 0 none weight 0 :60" | dmsetup create ioband3
+             # echo "0 $(blockdev --getsize /dev/sdb4) ioband /dev/sdb4 2" \
+               "0 0 none weight 0 :40" | dmsetup create ioband4
+
+
+   --------------------------------------------------------------------------
+
+  Remove the ioband device
+
+   SYNOPSIS
+
+           dmsetup remove IOBAND_DEVICE
+
+   DESCRIPTION
+
+             Remove the specified ioband device IOBAND_DEVICE. All the band
+           groups attached to the ioband device are also removed
+           automatically.
+
+   EXAMPLE
+
+             Remove ioband device "ioband1."
+
+             # dmsetup remove ioband1
+
+
+   --------------------------------------------------------------------------
+
+  Set an ioband group type
+
+   SYNOPSIS
+
+           dmsetup message IOBAND_DEVICE 0 type TYPE
+
+   DESCRIPTION
+
+             Set the ioband group type of the specified ioband device
+           IOBAND_DEVICE. TYPE must be one of "none", "user", "gid", "pid" or
+           "pgrp." Once the type is set, new ioband groups can be created on
+           IOBAND_DEVICE.
+
+   EXAMPLE
+
+             Set the ioband group type of ioband device "ioband1" to "user."
+
+             # dmsetup message ioband1 0 type user
+
+
+   --------------------------------------------------------------------------
+
+  Create an ioband group
+
+   SYNOPSIS
+
+           dmsetup message IOBAND_DEVICE 0 attach ID
+
+   DESCRIPTION
+
+             Create an ioband group and attach it to IOBAND_DEVICE. ID
+           specifies user-id, group-id, process-id or process-group-id
+           depending the ioband group type of IOBAND_DEVICE.
+
+   EXAMPLE
+
+             Create an ioband group which consists of all processes with
+           user-id 1000 and attach it to ioband device "ioband1."
+
+             # dmsetup message ioband1 0 type user
+             # dmsetup message ioband1 0 attach 1000
+
+
+   --------------------------------------------------------------------------
+
+  Detach the ioband group
+
+   SYNOPSIS
+
+           dmsetup message IOBAND_DEVICE 0 detach ID
+
+   DESCRIPTION
+
+             Detach the ioband group specified by ID from ioband device
+           IOBAND_DEVICE.
+
+   EXAMPLE
+
+             Detach the ioband group with ID "2000" from ioband device
+           "ioband2."
+
+             # dmsetup message ioband2 0 detach 1000
+
+
+   --------------------------------------------------------------------------
+
+  Set the weight of an ioband group
+
+   SYNOPSIS
+
+           dmsetup message IOBAND_DEVICE 0 weight VAL
+
+           dmsetup message IOBAND_DEVICE 0 weight ID:VAL
+
+   DESCRIPTION
+
+             Set the weight of the ioband group specified by ID. Set the
+           weight of the default ioband group of IOBAND_DEVICE if ID isn't
+           specified.
+
+             The following example means that "ioband1" can use 80% ---
+           40/(40+10)*100 --- of the bandwidth of the physical disk while
+           "ioband2" can use 20%.
+
+             # dmsetup message ioband1 0 weight 40
+             # dmsetup message ioband2 0 weight 10
+
+
+             The following lines have the same effect as the above:
+
+             # dmsetup message ioband1 0 weight 4
+             # dmsetup message ioband2 0 weight 1
+
+
+             VAL must be an integer larger than 0. The default value, which
+           is assigned to newly created ioband groups, is 100.
+
+   EXAMPLE
+
+             Set the weight of the default ioband group of "ioband1" to 40.
+
+             # dmsetup message ioband1 0 weight 40
+
+
+             Set the weight of the ioband group of "ioband1" with ID "1000"
+           to 10.
+
+             # dmsetup message ioband1 0 weight 1000:10
+
+
+   --------------------------------------------------------------------------
+
+  Set the number of tokens
+
+   SYNOPSIS
+
+           dmsetup message IOBAND_DEVICE 0 token VAL
+
+   DESCRIPTION
+
+             Set the number of tokens to VAL. According to their weight, this
+           number of tokens will be distributed to all the ioband groups on
+           the physical device to which ioband device IOBAND_DEVICE belongs
+           when they use up their tokens.
+
+             VAL must be an integer greater than 0. The default is 2048.
+
+   EXAMPLE
+
+             Set the number of tokens of the physical device to which
+           "ioband1" belongs to 256.
+
+             # dmsetup message ioband1 0 token 256
+
+
+   --------------------------------------------------------------------------
+
+  Set I/O throttling
+
+   SYNOPSIS
+
+           dmsetup message IOBAND_DEVICE 0 io_throttle VAL
+
+   DESCRIPTION
+
+             Set the I/O throttling value of the physical disk to which
+           ioband device IOBAND_DEVICE belongs to VAL. Dm-ioband start to
+           control the bandwidth when the number of BIOs in progress on the
+           physical disk exceeds this value.
+
+   EXAMPLE
+
+             Set the I/O throttling value of "ioband1" to 16.
+
+             # dmsetup message ioband1 0 io_throttle 16
+
+
+   --------------------------------------------------------------------------
+
+  Set I/O limiting
+
+   SYNOPSIS
+
+           dmsetup message IOBAND_DEVICE 0 io_limit VAL
+
+   DESCRIPTION
+
+             Set the I/O limiting value of the physical disk to which ioband
+           device IOBAND_DEVICE belongs to VAL. Dm-ioband will block all I/O
+           requests for the physical device if the number of BIOs in progress
+           on the physical disk exceeds this value.
+
+   EXAMPLE
+
+             Set the I/O limiting value of "ioband1" to 128.
+
+             # dmsetup message ioband1 0 io_limit 128
+
+
+   --------------------------------------------------------------------------
+
+  Display settings
+
+   SYNOPSIS
+
+           dmsetup table --target ioband
+
+   DESCRIPTION
+
+             Display the current table for the ioband device in a format. See
+           "dmsetup create" command for information on the table format.
+
+   EXAMPLE
+
+             The following output shows the current table of "ioband1."
+
+             # dmsetup table --target ioband
+             ioband: 0 32129937 ioband1 8:29 128 10 400 user weight \
+               2048 :100 1000:80 2000:20
+
+
+   --------------------------------------------------------------------------
+
+  Display Statistics
+
+   SYNOPSIS
+
+           dmsetup status --target ioband
+
+   DESCRIPTION
+
+             Display the statistics of all the ioband devices whose target
+           type is "ioband."
+
+             The output format is as below. the first five columns shows:
+
+              *   ioband device name
+
+              *   logical start sector of the device (must be 0)
+
+              *   device size in sectors
+
+              *   target type (must be "ioband")
+
+              *   device group ID
+
+             The remaining columns show the statistics of each ioband group
+           on the band device. Each group uses seven columns for its
+           statistics.
+
+              *   ioband group ID (-1 means default)
+
+              *   total read requests
+
+              *   delayed read requests
+
+              *   total read sectors
+
+              *   total write requests
+
+              *   delayed write requests
+
+              *   total write sectors
+
+   EXAMPLE
+
+             The following output shows the statistics of two ioband devices.
+           Ioband2 only has the default ioband group and ioband1 has three
+           (default, 1001, 1002) ioband groups.
+
+             # dmsetup status
+             ioband2: 0 44371467 ioband 128 -1 143 90 424 122 78 352
+             ioband1: 0 44371467 ioband 128 -1 223 172 408 211 136 600 1001 \
+             166 107 472 139 95 352 1002 211 146 520 210 147 504
+
+
+   --------------------------------------------------------------------------
+
+  Reset status counter
+
+   SYNOPSIS
+
+           dmsetup message IOBAND_DEVICE 0 reset
+
+   DESCRIPTION
+
+             Reset the statistics of ioband device IOBAND_DEVICE.
+
+   EXAMPLE
+
+             Reset the statistics of "ioband1."
+
+             # dmsetup message ioband1 0 reset
+
+
+   --------------------------------------------------------------------------
+
+Examples
+
+  Example #1: Bandwidth control on Partitions
+
+     This example describes how to control the bandwidth with disk
+   partitions. The following diagram illustrates the configuration of this
+   example. You may want to run a database on /dev/mapper/ioband1 and web
+   applications on /dev/mapper/ioband2.
+
+                 /mnt1                        /mnt2            mount points
+                   |                              |
+     +-------------V------------+ +-------------V------------+
+     |   /dev/mapper/ioband1    | |   /dev/mapper/ioband2    | ioband devices
+     +--------------------------+ +--------------------------+
+     |       default group      | |       default group      | ioband groups
+     |           (80)           | |           (40)           |    (weight)
+     +-------------|------------+ +-------------|------------+
+                   |                            |
+     +-------------V-------------+--------------V------------+
+     |         /dev/sda1         |          /dev/sda2        | physical devices
+     +---------------------------+---------------------------+
+
+
+     To setup the above configuration, follow these steps:
+
+    1.   Create ioband devices with the same device group ID and assign
+       weights of 80 and 40 to the default ioband groups respectively.
+
+         # echo "0 $(blockdev --getsize /dev/sda1) ioband /dev/sda1 1 0 0" \
+             "none weight 0 :80" | dmsetup create ioband1
+         # echo "0 $(blockdev --getsize /dev/sda2) ioband /dev/sda2 1 0 0" \
+             "none weight 0 :40" | dmsetup create ioband2
+
+
+    2.   Create filesystems on the ioband devices and mount them.
+
+         # mkfs.ext3 /dev/mapper/ioband1
+         # mount /dev/mapper/ioband1 /mnt1
+
+         # mkfs.ext3 /dev/mapper/ioband2
+         # mount /dev/mapper/ioband2 /mnt2
+
+
+   --------------------------------------------------------------------------
+
+  Example #2: Bandwidth control on Logical Volumes
+
+     This example is similar to the example #1 but it uses LVM logical
+   volumes instead of disk partitions. This example shows how to configure
+   ioband devices on two striped logical volumes.
+
+                 /mnt1                        /mnt2            mount points
+                   |                            |
+     +-------------V------------+ +-------------V------------+
+     |   /dev/mapper/ioband1    | |   /dev/mapper/ioband2    | ioband devices
+     +--------------------------+ +--------------------------+
+     |       default group      | |       default group      | ioband groups
+     |           (80)           | |           (40)           |    (weight)
+     +-------------|------------+ +-------------|------------+
+                   |                            |
+     +-------------V------------+ +-------------V------------+
+     |      /dev/mapper/lv0     | |     /dev/mapper/lv1      | striped logical
+     |                          | |                          | volumes
+     +-------------------------------------------------------+
+     |                          vg0                          | volume group
+     +-------------|----------------------------|------------+
+                   |                            |
+     +-------------V------------+ +-------------V------------+
+     |         /dev/sdb         | |         /dev/sdc         | physical devices
+     +--------------------------+ +--------------------------+
+
+
+     To setup the above configuration, follow these steps:
+
+    1.   Initialize the partitions for use by LVM.
+
+         # pvcreate /dev/sdb
+         # pvcreate /dev/sdc
+
+
+    2.   Create a new volume group named "vg0" with /dev/sdb and /dev/sdc.
+
+         # vgcreate vg0 /dev/sdb /dev/sdc
+
+
+    3.   Create two logical volumes in "vg0." The volumes have to be striped.
+
+         # lvcreate -n lv0 -i 2 -l 64 vg0 -L 1024M
+         # lvcreate -n lv1 -i 2 -l 64 vg0 -L 1024M
+
+
+         The rest is the same as the example #1.
+
+    4.   Create ioband devices corresponding to each logical volume and
+       assign weights of 80 and 40 to the default ioband groups respectively.
+
+         # echo "0 $(blockdev --getsize /dev/mapper/vg0-lv0)" \
+            "ioband /dev/mapper/vg0-lv0 1 0 0 none weight 0 :80" | \
+            dmsetup create ioband1
+         # echo "0 $(blockdev --getsize /dev/mapper/vg0-lv1)" \
+            "ioband /dev/mapper/vg0-lv1 1 0 0 none weight 0 :40" | \
+            dmsetup create ioband2
+
+
+    5.   Create filesystems on the ioband devices and mount them.
+
+         # mkfs.ext3 /dev/mapper/ioband1
+         # mount /dev/mapper/ioband1 /mnt1
+
+         # mkfs.ext3 /dev/mapper/ioband2
+         # mount /dev/mapper/ioband2 /mnt2
+
+
+   --------------------------------------------------------------------------
+
+  Example #3: Bandwidth control on processes
+
+     This example describes how to control the bandwidth with groups of
+   processes. You may also want to run an additional application on the same
+   machine described in the example #1. This example shows how to add a new
+   ioband group for this application.
+
+                 /mnt1                        /mnt2            mount points
+                   |                            |
+     +-------------V------------+ +-------------V------------+
+     |   /dev/mapper/ioband1    | |   /dev/mapper/ioband2    | ioband devices
+     +-------------+------------+ +-------------+------------+
+     |          default         | |  user=1000  |   default  | ioband groups
+     |           (80)           | |     (20)    |    (40)    |   (weight)
+     +-------------+------------+ +-------------+------------+
+                   |                            |
+     +-------------V-------------+--------------V------------+
+     |         /dev/sda1         |          /dev/sda2        | physical device
+     +---------------------------+---------------------------+
+
+
+     The following shows to set up a new ioband group on the machine that is
+   already configured as the example #1. The application will have a weight
+   of 20 and run with user-id 1000 on /dev/mapper/ioband2.
+
+    1.   Set the type of ioband2 to "user."
+
+         # dmsetup message ioband2 0 type user.
+
+
+    2.   Create a new ioband group on ioband2.
+
+         # dmsetup message ioband2 0 attach 1000
+
+
+    3.   Assign weight of 10 to this newly created ioband group.
+
+         # dmsetup message ioband2 0 weight 1000:20
+
+
+   --------------------------------------------------------------------------
+
+  Example #4: Bandwidth control for Xen virtual block devices
+
+     This example describes how to control the bandwidth for Xen virtual
+   block devices. The following diagram illustrates the configuration of this
+   example.
+
+           Virtual Machine 1            Virtual Machine 2      virtual machines
+                   |                            |
+     +-------------V------------+ +-------------V------------+
+     |         /dev/xvda1       | |         /dev/xvda1       | virtual block
+     +-------------|------------+ +-------------|------------+    devices
+                   |                            |
+     +-------------V------------+ +-------------V------------+
+     |   /dev/mapper/ioband1    | |   /dev/mapper/ioband2    | ioband devices
+     +--------------------------+ +--------------------------+
+     |       default group      | |       default group      | ioband groups
+     |           (80)           | |           (40)           |    (weight)
+     +-------------|------------+ +-------------|------------+
+                   |                            |
+     +-------------V-------------+--------------V------------+
+     |         /dev/sda1         |          /dev/sda2        | physical device
+     +---------------------------+---------------------------+
+
+
+     The followings shows how to map ioband device "ioband1" and "ioband2" to
+   virtual block device "/dev/xvda1 on Virtual Machine 1" and "/dev/xvda1 on
+   Virtual Machine 2" respectively on the machine configured as the example
+   #1. Add the following lines to the configuration files that are referenced
+   when creating "Virtual Machine 1" and "Virtual Machine 2."
+
+       For "Virtual Machine 1"
+       disk = [ 'phy:/dev/mapper/ioband1,xvda,w' ]
+
+       For "Virtual Machine 2"
+       disk = [ 'phy:/dev/mapper/ioband2,xvda,w' ]
+
+
+   --------------------------------------------------------------------------
+
+  Example #5: Bandwidth control for Xen blktap devices
+
+     This example describes how to control the bandwidth for Xen virtual
+   block devices when Xen blktap devices are used. The following diagram
+   illustrates the configuration of this example.
+
+           Virtual Machine 1            Virtual Machine 2      virtual machines
+                   |                            |
+     +-------------V------------+ +-------------V------------+
+     |         /dev/xvda1       | |         /dev/xvda1       | virtual block
+     +-------------|------------+ +-------------|------------+    devices
+                   |                            |
+     +-------------V----------------------------V------------+
+     |                  /dev/mapper/ioband1                  | ioband device
+     +---------------------------+---------------------------+
+     |       default group       |        default group      | ioband groups
+     |           (80)            |            (40)           |    (weight)
+     +-------------|-------------+--------------|------------+
+                   |                            |
+     +-------------|----------------------------|------------+
+     |  +----------V----------+      +----------V---------+  |
+     |  |       vm1.img       |      |       vm2.img      |  | disk image files
+     |  +---------------------+      +--------------------+  |
+     |                        /vmdisk                        | mount point
+     +---------------------------|---------------------------+
+                                 |
+     +---------------------------V---------------------------+
+     |                       /dev/sda1                       | physical device
+     +-------------------------------------------------------+
+
+
+     To setup the above configuration, follow these steps:
+
+    1.   Create an ioband device.
+
+         # echo "0 $(blockdev --getsize /dev/sda1) ioband /dev/sda1" \
+             "1 0 0 none weight 0 :100" | dmsetup create ioband1
+
+
+    2.   Add the following lines to the configuration files that are
+       referenced when creating "Virtual Machine 1" and "Virtual Machine 2."
+       Disk image files "/vmdisk/vm1.img" and "/vmdisk/vm2.img" will be used.
+
+         For "Virtual Machine 1"
+         disk = [ 'tap:aio:/vmdisk/vm1.img,xvda,w', ]
+
+         For "Virtual Machine 1"
+         disk = [ 'tap:aio:/vmdisk/vm2.img,xvda,w', ]
+
+
+    3.   Run the virtual machines.
+
+         # xm create vm1
+         # xm create vm2
+
+
+    4.   Find out the process IDs of the daemons which control the blktap
+       devices.
+
+         # lsof /vmdisk/disk[12].img
+         COMMAND   PID USER   FD   TYPE DEVICE       SIZE  NODE NAME
+         tapdisk 15011 root   11u   REG  253,0 2147483648 48961 /vmdisk/vm1.img
+         tapdisk 15276 root   13u   REG  253,0 2147483648 48962 /vmdisk/vm2.img
+
+
+    5.   Create new ioband groups of pid 15011 and pid 15276, which are
+       process IDs of the tapdisks, and assign weight of 80 and 40 to the
+       groups respectively.
+
+         # dmsetup message ioband1 0 type pid
+         # dmsetup message ioband1 0 attach 15011
+         # dmsetup message ioband1 0 weight 15011:80
+         # dmsetup message ioband1 0 attach 15276
+         # dmsetup message ioband1 0 weight 15276:40
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