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Multipath Device Configuration, Traditional Multipath Device Configurations

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If you created iface records for specific adapters, ehcmd uses the existing records. If ehcmd creates new records, it uses the naming scheme eql.eth0_X. For example: # iscsiadm -m iface | sort default tcp,,,, eql.eth0_0 tcp,00:26:B9:3A:6B:9E,,, eql.eth0_1 tcp,00:26:B9:3A:6B:9E,,, eql.eth1_0 tcp,00:26:B9:3A:6B:9F,,, eql.eth1_1 tcp,00:26:B9:3A:6B:9F,,, eql.eth2_0 tcp,00:1B:21:46:5E:18,,, eql.eth2_1 tcp,00:1B:21:46:5E:18,,, eql.eth3_0 tcp,00:1B:21:46:5E:19,,, eql.eth3_1 tcp,00:1B:21:46:5E:19,,, iser iser,,,, To avoid interrupting access to any iSCSI storage, these additional iSCSI interfaces will be left in place if the HIT/Linux software is ever uninstalled. Multipath Device Configuration When you configure multipath device I/O, a mounted volume on a host is shown as a single disk. MPIO configuration uses multiple iSCSI sessions to the SAN volume to provide load balancing and ensure that I/O operations, such as writing data to a volume, succeed even if there is a network error. Traditional Multipath Device Configurations Traditional multipath configurations are implemented as a single tier of Device Mapper multipath devices. These configurations spread I/O sent to the multipath device to the constituent SCSI disk (SD) block devices. Multipath Configuration A PS Series volume can have data spread across multiple group members. Multipath device configuration in HIT/Linux improves performance over standard Linux multipathing by ensuring the host has iSCSI sessions to each member. Using information about the volume layout, it routes each I/O directly to the destination group member, reducing the amount of I/O forwarding that is necessary between members. HIT/Linux includes two components that use this configuration: • The EqualLogic Host Connection Manager daemon (ehcmd) monitors the iSCSI session state and the configuration of the Linux server and PS Series group. Running in the background, ehcmd uses the Open-iSCSI management tool (iscsiadm) to add, remove, or modify iSCSI sessions to maintain optimal iSCSI sessions, and gathers information on the volume layout from the PS Series group. • A loadable kernel module, dm-switch, which implements a new Device Mapper target to the multipath devices. Based on the volume layout on the group members, the dm-switch module routes each I/O to the optimal path to the PS Series group. The result is a two-tier device structure for each volume with multiple multipath devices: one for each member containing a portion of the volume and a switch device on top of the multipath devices. The following figure shows the relevant components in the storage stack. Configuring Multipath I/O Devices 33

Section	Page
Dell EqualLogic Host Integration Tools for Linux Version 1.7 Installation and User’s Guide	3
About This Guide	8
Revision History	8
Audience	8
Related Documentation	8
Dell Online Services	8
Technical Support and Customer Service	8
Contacting Dell	8
Introduction to HIT/Linux	9
Overview	9
Terminology	9
PS Series Group Network Recommendations	10
Installing and Configuring HIT/Linux	11
Obtain the Installation Kit	11
Installation Prerequisites	11
Installation Script and RPMs	11
Dell End-User License Agreement (EULA)	12
Supported Linux Distributions	12
Array Firmware	12
Supported File Systems	12
Use of the multipathd Daemon	12
Linux Packages and Dependencies	13
Installation Procedure	13
Pre-Installation Steps	13
Installation Steps	14
Installation Results	14
Uninstalling HIT/Linux	16
Updating HIT/Linux	16
Configuration	16
Configuring HIT/Linux	17
Step 1: Verify Configurable Parameters with eqltune and eqlconfig	17
Step 2: Verify Bash Command Line Completion is Configured	17
Step 3: View and Modify MPIO Configuration Settings	17
Step 4: Enable or Disable Multipath I_O	17
Step 5: Discover iSCSI Targets and Create Sessions to Volumes	17
EqualLogic Configuration Utility (eqlconfig)	17
EqualLogic Host Performance and Tuning Suite (eqltune)	18
Features	18
eqlconfig Command Syntax	18
eqltune Command Syntax	19
Evaluating Output Information	19
Block Devices	19
Sysctl Tunables	20
Ethernet Devices	20
iSCSI Settings	20
Logical Volume Management (LVM)	20
EqualLogic Host Tools	20
Examples: eqltune Output	20
Configuring ASM/LE	21
Environment Prerequisites	22
Group Requirements	22
Access to Volumes and Snapshots	22
Verification	22
Remote Setup Wizard Command Line Interface	23
General Command Syntax for the RSWCLI	23
Configuration — Discovering a PS Series Array	23
rswcli --discover Command Syntax	24
Example: Discovering Uninitialized PS Series Arrays	24
Initializing a PS Series Array	24
rswcli --initialize Command Syntax	24
Example: Initializing a PS Series Array	26
Managing Access to a PS Series Group	26
Adding Access to a Group	26
rswcli --add-group-access Command Syntax	26
Example: Adding Group Access	27
Listing Accessible Groups	27
rswcli --list-group Command Syntax	27
Example: Listing Information for Groups	28
Modifying Access to a Group	28
rswcli --modify-group-access Command Syntax	28
Example: Modifying Group Access	28
Removing Host Access to a Group	29
rswcli --remove-group-access Command Syntax	29
Example: Removing Host Access to Group	29
Configuring Multipath I/O	29
Configuring Multipath I/O Devices	30
Accessing Volumes Using Multipath I/O	30
Discovering Targets	30
Log In to an MPIO Volume	31
Logging In to an MPIO Volume	31
Mount an MPIO Volume	31
Logging Out of an MPIO Volume	32
Displaying Connections to a Volume	32
Managing Automatic Logins	32
Managing iSCSI Interfaces	32
Multipath Device Configuration	33
Traditional Multipath Device Configurations	33
Multipath Configuration	33
Example Multipath Device Configuration	35
Special MPIO Configuration Cases	35
Conditions for Configuring Multipath Devices	36
Use of the multipathd Daemon	36
Use of dm-switch Kernel Module	36
Configuring Settings for Multipath I/O	37
Multipath I/O Sessions	37
Setting MPIO Parameters	37
Listing MPIO Subnets	37
rswcli --mpio-parameters Command Syntax	37
Examples: Setting MPIO Parameters	38
rswcli --mpio-list Command Syntax	39
Example: Listing Included MPIO Subnets	39
Including a Subnet or Adapter for MPIO	39
rswcli --mpio-include Command Syntax	39
Examples: mpio-include Command	40
Excluding a Subnet or Adapter From MPIO	41
Including or Excluding Specific Host NICs	41
Configuring I/O Path Selection	41
Load Balancing Policy	41
I/O Scheduling	41
Setting Volume-Specific Configuration Parameters	41
Introduction to ASM/LE	43
About ASM/LE	43
About Smart Copies	43
Types of Smart Copies Created	44
Snapshot Smart Copies	44
Replica Smart Copies	44
Clone Smart Copies	45
Replica Clones	45
Thin Clone Smart Copies	45
Synchronous Replication and Smart Copies	45
Select a Smart Copy	45
Requirements for Creating Smart Copies	46
About Snapshot Space Borrowing	46
Methods of Creating Smart Copies	46
About Group Access Files	47
About Collections	47
About Smart Copy Schedules	48
Advantages of Smart Copy Schedules	48
Constraints of Smart Copy Schedules	48
Data Restoration	48
About Mounting Smart Copies	49
About Unmounting Smart Copies	49
About Logging In to Smart Copies	49
About Logging Off Smart Copies	49
About Restoring Data From a Smart Copy	50
Preconditions for Restoring Data	50
Restoring Data Process	50
About Restoring a Soft-Deleted Smart Copy	50
About Managing Smart Copy Clones After Changing or Deleting Credentials	51
Example	51
Best Practices For Using ASM/LE	53
Auto-Snapshot Manager Command Line Interface	54
Introduction to ASMCLI	54
Entering ASMCLI Commands	54
General Command Syntax for ASMCLI	54
Access Help on ASMCLI Commands	55
ASMCLI Search Options	55
Creating and Managing Group Access Files	57
Creating Access to a PS Series Group	57
asmcli create group-access Command Syntax	57
Examples: Creating Group Access	58
Listing Group Access Information	60
asmcli list group-access Command Syntax	60
Examples: Listing Group Access Information	60
Updating Access to a Group	61
asmcli update group-access Command Syntax	61
Examples: Updating Group Access Information	62
Deleting Group Access Information	63
asmcli delete group-access Command Syntax	63
Examples: Deleting Group Access Information	63
Creating and Managing Smart Copies	64
Creating a Smart Copy the First Time	64
Creating a Smart Copy	64
asmcli create smart-copy Command Syntax	64
Examples: Creating Smart Copies	66
Listing Available Smart Copies	70
asmcli list smart-copy Command Syntax	70
Examples: Listing Smart Copies	70
Access Backup Documents	72
Deleting a Smart Copy	72
asmcli delete smart-copy Command Syntax	72
Examples: Deleting Smart Copies	73
Restoring a Smart Copy	74
asmcli restore smart-copy Command Syntax	75
Example: Restoring Smart Copies	75
Soft-Deleted Smart Copies	75
Managing Soft-Deleted Smart Copies	76
Examples: asmcli list Command	76
Managing Soft-Deleted Smart Copy Clones Without Credentials	77
Smart Copy Operations for Synchronous Replication Volumes	77
Example: Attempting to Restore a Snapshot Created on the Alternate Volume	78
Creating and Managing Smart Copy Schedules	78
Creating a Schedule	79
asmcli create schedule Command Syntax	79
Example: Creating Schedules	80
Listing Schedules	80
asmcli list schedule Command Syntax	80
Examples: Listing Schedules	81
Running a Schedule	83
asmcli do schedule Command Syntax	83
Examples: Running Schedules	83
Updating a Schedule	84
asmcli update schedule Command Syntax	84
Examples: Updating Schedules	86
Deleting a Schedule	87
asmcli delete schedule Command Syntax	87
Example: Deleting a Schedule	87
Mounting and Unmounting Smart Copies	88
Mounting a Smart Copy	88
Mounting Read-Only Smart Copies	88
asmcli mount smart-copy Command Syntax	89
Example: Mounting a Smart Copy	89
Unmounting a Smart Copy	89
asmcli unmount smart-copy Command Syntax	90
Example: Unmounting a Smart Copy	90
Logging In to and Out of Smart Copies	91
Logging In to a Smart Copy	91
asmcli login smart-copy Command Syntax	91
Example: Logging In to Smart Copies	92
Logging Out of a Smart Copy	92
asmcli logout smart-copy Command Syntax	92
Example: Specifying an Object ID with Logout	93
Creating and Managing Collections	93
Creating a Collection	93
asmcli create collection Command Syntax	94
Example: Creating Collections	94
Listing Collections	94
asmcli list collection Command Syntax	94
Example: Listing Collections	95
Updating a Collection	95
asmcli update collection Command Syntax	95
Examples: Updating Collections	95
Deleting a Collection	96
asmcli delete collection Command Syntax	96
Example: Deleting Collections	96
Managing Thin-Provisioned Volumes	97
About Thin-Provisioning	97
Realtime Thin-Provisioning	97
On-Demand Thin-Provisioning	98
Thin-Provisioning as Scheduled Maintenance	98
Group Access Files	99
Considerations for Thin-Provisioning	99
File System and Volume Characteristics	99
Multiple File Systems	99
Volume Thin-Provisioning Configuration Parameters	100
Show Mount Point Information	100
eqlvolume show Command Syntax	101
Examples: Showing Mount Point Information	101
Thin-Provisioning a Volume	102
eqlvolume rethin Command Syntax	103
Examples: Analyzing Thin—Provisioning Recommendations	103
Troubleshooting	105
General Troubleshooting Guidelines	105
Ensuring Correct Operation of the dm-switch Kernel Module	105
Establishing iSCSI Sessions	105
Increasing the Volume Size on a PS Series Group	105
Logical Volume Manager (LVM) Considerations	106
LVM Filtering Rules for EqualLogic Devices	106
Verify and Fix LVM Filters with eqltune	106
Linux Distribution-Specific udev Rule Considerations	107
Considerations when Using the Auto-Snapshot Manager CLI	107
Logical Volume Manager and Read-Only Media	107
Logical Volume Manager and Promoted Replica Volumes	107
Using the eqllog Facility	108
Command Syntax	108
Example: eqllog Output	108
Using the udev Facility	109
Using the ehcmcli Diagnostic Tool	110
ehcmcli Command Syntax	110
ehcmcli Diagnostic Output	111
Running the ehcmd Daemon	112
Considerations When Partitioning iSCSI Volumes	113
Migrating to HIT Linux Multipath I/O	114
Before You Begin	114
Step 1: Install HIT Linux in Migration Mode	114
Step 2: Migrate Existing Storage-Using Applications	115
Logical Volume Manager Considerations	115
Directly Mounted File Systems	115
Block Device Access	116
Excluding Specific Volumes	116
Step 3: Reconfigure multipathd	116
Step 4: Complete the Installation	116
Disabling Active Management	117
Enabling Storage Cluster Support	117
Cluster Logical Volume Manager	117
Enabling iSCSI Offload on HIT/Linux	118
Step 1: Set Up and Verify Your Configuration	118
Step 2: Configure the Network Interfaces	118
Step 3: Configure ehcmd to Use the Offload iSCSI Initiator	119
Step 4: Discover iSCSI Targets	119
Step 5: Logging In to Additional Targets	120
Bash Command Completion	121
DKMS Considerations for Red Hat Linux	123
Index	124
A	124
B	124
C	124
D	124
E	124
F	125
G	125
H	125
I	125
K	125
L	125
M	125
N	126
P	126
R	126
S	126
T	126
U	126

Match case Limit results 1 per page

If you created iface records for specific adapters, ehcmd uses the existing records. If ehcmd creates new records, it uses the naming

scheme

eql.eth0_X

. For example:

# iscsiadm -m iface | sort

default tcp,<empty>,<empty>,<empty>,<empty>

eql.eth0_0 tcp,00:26:B9:3A:6B:9E,<empty>,<empty>,<empty>

eql.eth0_1 tcp,00:26:B9:3A:6B:9E,<empty>,<empty>,<empty>

eql.eth1_0 tcp,00:26:B9:3A:6B:9F,<empty>,<empty>,<empty>

eql.eth1_1 tcp,00:26:B9:3A:6B:9F,<empty>,<empty>,<empty>

eql.eth2_0 tcp,00:1B:21:46:5E:18,<empty>,<empty>,<empty>

eql.eth2_1 tcp,00:1B:21:46:5E:18,<empty>,<empty>,<empty>

eql.eth3_0 tcp,00:1B:21:46:5E:19,<empty>,<empty>,<empty>

eql.eth3_1 tcp,00:1B:21:46:5E:19,<empty>,<empty>,<empty>

iser iser,<empty>,<empty>,<empty>,<empty>

To avoid interrupting access to any iSCSI storage, these additional iSCSI interfaces will be left in place if the HIT/Linux software is ever

uninstalled.

Multipath Device Configuration

When you configure multipath device I/O, a mounted volume on a host is shown as a single disk. MPIO configuration uses multiple iSCSI

sessions to the SAN volume to provide load balancing and ensure that I/O operations, such as writing data to a volume, succeed even if

there is a network error.

Traditional Multipath Device Configurations

Traditional multipath configurations are implemented as a single tier of Device Mapper multipath devices. These configurations spread I/O

sent to the multipath device to the constituent SCSI disk (SD) block devices.

Multipath Configuration

A PS Series volume can have data spread across multiple group members. Multipath device configuration in HIT/Linux improves

performance over standard Linux multipathing by ensuring the host has iSCSI sessions to each member. Using information about the

volume layout, it routes each I/O directly to the destination group member, reducing the amount of I/O forwarding that is necessary

between members.

HIT/Linux includes two components that use this configuration:

•

The EqualLogic Host Connection Manager daemon (ehcmd) monitors the iSCSI session state and the configuration of the Linux server

and PS Series group. Running in the background, ehcmd uses the Open-iSCSI management tool (iscsiadm) to add, remove, or modify

iSCSI sessions to maintain optimal iSCSI sessions, and gathers information on the volume layout from the PS Series group.

•

A loadable kernel module,

dm-switch

, which implements a new Device Mapper target to the multipath devices. Based on the volume

layout on the group members, the

dm-switch

module routes each I/O to the optimal path to the PS Series group.

The result is a two-tier device structure for each volume with multiple multipath devices: one for each member containing a portion of the

volume and a switch device on top of the multipath devices.

The following figure shows the relevant components in the storage stack.

Configuring Multipath I/O Devices