Dell EqualLogic PS6210XS EqualLogic Host Integration Tools for Linux Version 1 - Page 37

Configuring Settings for Multipath I/O, Multipath I/O Sessions, Setting MPIO Parameters

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For additional information troubleshooting problems with the dm-switch kernel module, see Assuring Correct Operation of the dmswitch Kernel Module. Configuring Settings for Multipath I/O HIT/Linux lets you configure multiple multipath devices as redundant paths from a Linux iSCSI initiator to a PS Series volume. RSWCLI commands for Multipath I/O (MPIO) let you: • Set MPIO parameters • List MPIO parameters • Include a subnet for use by MPIO • Exclude a subnet for use by MPIO Multipath I/O Sessions The number of paths created by HIT/Linux MPIO depends on the topology of your SAN and the MPIO settings on the host computer. Every volume is distributed across one or more members in the PS Series group. The portion of a volume that is located on a single member is referred to as a volume slice. The ehcmd utility creates one or more iSCSI sessions to each volume slice. The actual number of sessions is determined through the following actions: 1. Calculating the optimal number of sessions to maximize the bandwidth between the host and the member. This calculation takes into account the speed of available host adapters and network interface cards (NICs) on each member hosting part of the volume. The algorithm does not create unnecessary sessions when there is no performance benefit. Therefore, in configurations with limited numbers of computer and member Ethernet ports, the actual number of sessions created might be fewer than the user limits specified in the next step. Example A: You have 2 x 1 Gb host NICs, and are connecting to a volume on members with 4 x 1 Gb eth ports. The optimal number of sessions is 2 per member, because that number saturates the host NICs. Example B: You have 1 x 10 Gb host NICs, and are connecting to a volume on members with 4 x 1 Gb eth ports. The optimal number of sessions is 4 per member, because that number saturates the member eth ports. Example C: You have 2 x 10 Gb host NICs, and are connecting to a volume on members with 1 x 10 Gb eth ports. The optimal number of sessions is 1 per member, because that number saturates the member eth ports. 2. Applying any user-configured session limits. The default behavior is to limit to 2 sessions per volume slice or 6 sessions per volume, whichever is reached first. However, you can modify these limits, as described in Setting MPIO Parameters. 3. Apply a per-pool throttle to ensure the group remains below 90% of the maximum number of allowed connections per pool. This throttling logic ensures the connections are equitably shared among all the pool members and all the hosts using HIT multipathing to connect to volumes on the group. See the Dell EqualLogic PS Series Storage Arrays Release Notes for the current configuration limits. Setting MPIO Parameters Use the rswcli --mpio-parameters (or rswcli -P) command to change the settings used for configuring MPIO. All parameters are optional. If you do not enter parameters for this command, the current values for all parameters are listed. Listing MPIO Subnets Use the rswcli --mpio-list (or rswcli -L) command to list the subnets that are included and excluded for use by MPIO. rswcli --mpio-parameters Command Syntax The command syntax is as follows: rswcli --mpio-parameters | -P [--max-sessions-per-entire-volume 1-12 | --maxvole] [--dlb | --default-load-balancing LQD|RR] [--ios | --io-per-path 1-1000] [--max-sessions-per-volume-slice 1-4 | --maxvols] [--minsp | --min-adapter-speed 100|1000|10000 (as Mbps)] [--msnap | --use-mpio-snapshots yes|no] [--ip | --useip or --ip6 | --useip6] The following table describes the optional command parameters. Configuring Multipath I/O Devices 37

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For additional information troubleshooting problems with the
dm-switch
kernel module, see
Assuring Correct Operation of the dm-
switch Kernel Module
.
Configuring Settings for Multipath I/O
HIT/Linux lets you configure multiple multipath devices as redundant paths from a Linux iSCSI initiator to a PS Series volume. RSWCLI
commands for Multipath I/O (MPIO) let you:
•
Set MPIO parameters
•
List MPIO parameters
•
Include a subnet for use by MPIO
•
Exclude a subnet for use by MPIO
Multipath I/O Sessions
The number of paths created by HIT/Linux MPIO depends on the topology of your SAN and the MPIO settings on the host computer.
Every volume is distributed across one or more members in the PS Series group. The portion of a volume that is located on a single
member is referred to as a
volume slice
. The ehcmd utility creates one or more iSCSI sessions to each volume slice. The actual number of
sessions is determined through the following actions:
1.
Calculating the optimal number of sessions to maximize the bandwidth between the host and the member. This calculation takes into
account the speed of available host adapters and network interface cards (NICs) on each member hosting part of the volume. The
algorithm does not create unnecessary sessions when there is no performance benefit. Therefore, in configurations with limited
numbers of computer and member Ethernet ports, the actual number of sessions created might be fewer than the user limits specified
in the next step.
Example A: You have 2 x 1 Gb host NICs, and are connecting to a volume on members with 4 x 1 Gb eth ports. The optimal number of
sessions is 2 per member, because that number saturates the host NICs.
Example B: You have 1 x 10 Gb host NICs, and are connecting to a volume on members with 4 x 1 Gb eth ports. The optimal number of
sessions is 4 per member, because that number saturates the member eth ports.
Example C: You have 2 x 10 Gb host NICs, and are connecting to a volume on members with 1 x 10 Gb eth ports. The optimal number
of sessions is 1 per member, because that number saturates the member eth ports.
2.
Applying any user-configured session limits. The default behavior is to limit to 2 sessions per volume slice or 6 sessions per volume,
whichever is reached first. However, you can modify these limits, as described in
Setting MPIO Parameters
.
3.
Apply a per-pool throttle to ensure the group remains below 90% of the maximum number of allowed connections per pool. This
throttling logic ensures the connections are equitably shared among all the pool members and all the hosts using HIT multipathing to
connect to volumes on the group. See the
Dell EqualLogic PS Series Storage Arrays Release Notes
for the current configuration limits.
Setting MPIO Parameters
Use the
rswcli --mpio-parameters
(or
rswcli -P
) command to change the settings used for configuring MPIO. All parameters
are optional. If you do not enter parameters for this command, the current values for all parameters are listed.
Listing MPIO Subnets
Use the
rswcli --mpio-list
(or
rswcli -L
) command to list the subnets that are included and excluded for use by MPIO.
rswcli --mpio-parameters Command Syntax
The command syntax is as follows:
rswcli --mpio-parameters | -P
[--max-sessions-per-entire-volume
1-12
| --maxvole]
[--dlb | --default-load-balancing
LQD
|
RR
]
[--ios | --io-per-path
1-1000
]
[--max-sessions-per-volume-slice
1-4
| --maxvols]
[--minsp | --min-adapter-speed
100
|
1000
|
10000
(as Mbps)]
[--msnap | --use-mpio-snapshots
yes
|
no
]
[--ip | --useip or --ip6 | --useip6]
The following table describes the optional command parameters.
Configuring Multipath I/O Devices
37