Setting Up ISCSI Multipath In Ubuntu Server 12

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Setting up iSCSI Multipath in Ubuntu Server 12.04A Dell Technical White PaperJose De la RosaLinux Engineering

Dell IncSetting up iSCSI Multipath in Ubuntu Server 12.04THIS WHITE PAPER IS FOR INFORMATIONAL PURPOSES ONLY, AND MAY CONTAIN TYPOGRAPHICALERRORS AND TECHNICAL INACCURACIES. THE CONTENT IS PROVIDED AS IS, WITHOUT EXPRESS ORIMPLIED WARRANTIES OF ANY KIND. 2013 Dell Inc. All rights reserved. Reproduction of this material in any manner whatsoever withoutthe express written permission of Dell Inc. is strictly forbidden. For more information, contact Dell.Dell, the DELL logo, and the DELL badge, PowerConnect, and PowerVault are trademarks of Dell Inc.Symantec and the SYMANTEC logo are trademarks or registered trademarks of Symantec Corporation orits affiliates in the US and other countries. Microsoft, Windows, Windows Server, and Active Directoryare either trademarks or registered trademarks of Microsoft Corporation in the United States and/orother countries. Other trademarks and trade names may be used in this document to refer to either theentities claiming the marks and names or their products. Dell Inc. disclaims any proprietary interest intrademarks and trade names other than its own.August 20132

Dell IncSetting up iSCSI Multipath in Ubuntu Server 12.04Contents1.Introduction. 41.1 Purpose of this document . 41.2 Assumptions & Disclaimers . 41.3 Terms & Conventions . 42.Requirements . 42.1 Hardware . 42.2 Network Topology. 52.3 Network Configuration . 62.3.1 Reverse Path Filtering . 63.Setting up iSCSI connections . 74.Setting up Multipath . 105.Testing path failover . 126.Conclusion . 133

Dell IncSetting up iSCSI Multipath in Ubuntu Server 12.041. Introduction1.1 Purpose of this documentThis whitepaper describes how to setup and configure iSCSI Multipathing in Ubuntu Server 12.04using a Dell PowerEdge server and Dell EqualLogic storage. I don’t make recommendations orevaluate strategies for deploying a highly-available environment, but simply describe a step-by-stepset of instructions to give you a working deployment. I leave all final tweaks up to you.1.2 Assumptions & DisclaimersIt is assumed that the reader is familiar with iSCSI and multipathing concepts, as I do not discuss anytheory or concepts here. Expertise with iSCSI is not required to successfully follow these instructions;however some practical experience will make it easier understanding all steps.It is assumed that the reader is familiar with Ubuntu Server and with the Linux operating system ingeneral. You don’t have to be an expert, but some past background will be useful. I don’t coveradvanced topics such as booting from a multipath device or configuring a preseed file for automatedUbuntu installations onto a multipath device.It is assumed that you are familiar with Dell EqualLogic arrays and have experience managing them.I do not cover the steps needed to create and configure storage LUNs and I do not cover adding yourarray to pools and groups. All of this information can be found in the official documentation at I did not use the EqualLogic Host Integration Tools, you could potentially apply theseinstructions if you are instead using Dell PowerVault iSCSI arrays or software iSCSI targets hosted on aDell PowerEdge server. However, I only used Dell EqualLogic storage.1.3 Terms & Conventions LUN: iSCSI storage target on the storage array.Initiator: iSCSI client connecting to the iSCSI storage target (LUN).All commands are run as root. If you use a non-root account, prepend ‘sudo’ to each command.2. Requirements2.1 Hardware A Dell PowerEdge server with at least two network ports. For this whitepaper, I used different 11Gand 12G PowerEdge servers,One LUN on a Dell EqualLogic array (I used a PS4100E array). LUN capacity does not matter buttry with at least several hundred MBs. For simplicity purposes, I only used one array, which was amember of the default pool.4

Dell IncSetting up iSCSI Multipath in Ubuntu Server 12.042.2 Network TopologyThe ideal network configuration in a multipath environment is to connect each network port on yourserver to a different subnet. That way, you have additional resilience in case one of your subnets goesdown (i.e. bad switch or router). So ideally, you would have something like Figure 1:Dell PowerEdge serverNetworkPort 1NetworkPort 2NetworkPort 2NetworkPort 1Hard Drives0 1 2 34 5 6 78 9 10 11Dell EqualLogic arrayFigure 1: Multipath environment using one subnet per network portHowever, you can also connect both of your network ports to the same subnet if that is all you have,as depicted in Figure 2. In this case, your network subnet becomes a single point of failure, but youstill have high-availability capabilities in case one of your network ports fails. To increase resiliency inthis scenario, connect each network port to a different switch in your subnet.Dell PowerEdge serverNetworkPort 1NetworkPort 2NetworkPort 1NetworkPort 2Hard Drives0 1 2 34 5 6 78 9 10 11Dell EqualLogic arrayFigure 2: Multipath environment using one subnet for both network ports5

Dell IncSetting up iSCSI Multipath in Ubuntu Server 12.042.3 Network ConfigurationFor simplicity purposes, I used the network topology shown in Figure 2 with only one subnet. I have aClass C network ( and I used the following IP addresses:InterfaceServer network port 1Server network port 2EqualLogic Group portEqualLogic data port 1EqualLogic data port 2Interface nameeth0eth1eth0eth1IP 1.101192.168.1.102It’s up to you whether you use static IP addresses vs. DHCP. In this example I used static addresses fordemonstration purposes. Best practice documents don’t appear to prefer one method over the other,but my recommendation is to use static IP addresses since that’s what I used. If you use DHCP, besure you set the LUN access permissions accordingly. So for example if you are restricting access byIP address, restrict to “192.168.1.*”.The Group IP address is used for administrative and host access to your LUNs. It is the IP address thatwe will use in this whitepaper to communicate with the storage array. For details on how to configureyour array network ports, please refer to the official Dell EqualLogic documentation.2.3.1 Reverse Path FilteringYou might have to edit the reverse-path filter settings if you have problems pinging the Group IPthrough both of your network interfaces:# ping –I eth0 ping –I eth1 you get a response from both interfaces, then move on. Otherwise, you will have to change thissetting in /etc/sysctl.conf:net.ipv4.conf.eth0.rp filter 2net.ipv4.conf.eth1.rp filter 2If these entries are commented out, uncomment them and set to “2” as shown above (the defaultvalue is 1). Here’s a short snippet on values for this parameter:0: No source validation.1: Strict mode as defined in RFC3704 Strict Reverse Path. Each incoming packet is tested against theforwarding table and if the interface is not the best reverse path the packet check will fail. By defaultfailed packets are discarded.2: Loose mode as defined in RFC3704 Loose Reverse Path. Each incoming packet's source address isalso tested against the forwarding table and if the source address is not reachable via any interfacethe packet check will fail.After making the change and saving the file, load the new settings:6

ell IncSetting up iSCSI Multipath in Ubuntu Server 12.04# sysctl -p3. Setting up iSCSI connectionsBefore we setup multipathing, we must first establish the iSCSI connection to the LUN. In order towalk you through the iSCSI configuration process, we will illustrate with an example using the samesteps that I used in my lab.1.Install required packages:# apt-get install open-iscsi2.Assign a name to the initiator in /etc/iscsi/initiatorname.iscsi. The 'iscsi-iname' tool can be used togenerate a random initiator name that you can later add to the file, but the name already in theconfiguration file can also be used since it will already be unique. The file content will looksomething like this:InitiatorName parameters in /etc/iscsi/iscsid.conf:Edit node startup from 'manual' to 'automatic' so that logins to the iSCSI LUNs are automatic aftera system reboot:node.startup automaticIf you configured CHAP authentication in your Dell EqualLogic array, uncomment and edit theseparameters:node.session.auth.authmethod CHAPnode.session.auth.username chap-user node.session.auth.password chap-password Restart open-iscsi service so that new values take effect:# service open-iscsi restart4.Create iSCSI interfaces. To create the multiple logins for multipathing to work, we need to createan interface file for each network interface you wish to use to connect to the array.# iscsiadm -m iface -I eth0 -o new# iscsiadm -m iface -I eth1 -o newAdd interface name to each network port:# iscsiadm -m iface -I eth0 --op update -n ifacename -v eth0# iscsiadm -m iface -I eth1 --op update -n ifacename -v eth1Verify settings:7

Dell IncSetting up iSCSI Multipath in Ubuntu Server 12.04# iscsiadm -m iface -I eth0# BEGIN RECORD 2.0-871iface.iscsi ifacename ifacename eth0iface.ipaddress empty iface.hwaddress empty iface.transport name tcpiface.initiatorname empty # END RECORD# iscsiadm -m iface -I eth1# BEGIN RECORD 2.0-871iface.iscsi ifacename ifacename eth1iface.ipaddress empty iface.hwaddress empty iface.transport name tcpiface.initiatorname empty # END RECORD.You can leave the initiator, IP address and HW address fields empty.5.Discover LUN using the Group IP address:# iscsiadm -m discovery -t st -p,1 e9dc2d52096-dm-ubuntu192.168.1.100:3260,1 e9dc2d52096-dm-ubuntuThis will give you the target ID for your LUN (will be different for you). Since you have twoconnections to the iSCSI array, you should see the LUN listed twice.6.Login to LUN (replace target ID below with your own!):# iscsiadm -m node -T e9dc2d52096-dm-ubuntu –-loginLogging in to [iface: eth0, target: e9dc2d52096-dm-ubuntu, portal:,3260]Logging in to [iface: eth1, target: e9dc2d52096-dm-ubuntu, portal:,3260]Login to [iface: eth0, target: e9dc2d52096-dm-ubuntu, portal:,3260]: successfulLogin to [iface: eth1, target: e9dc2d52096-dm-ubuntu, portal:,3260]: successfulIf you list your storage devices with ‘fdisk –l”, you will see two additional storage devices. It’s thesame device, but it’s listed twice (one for each network port).7.Verify the iSCSI connections:# iscsiadm -m session -P 18

Dell IncSetting up iSCSI Multipath in Ubuntu Server 12.04Target: 3e9dc2d52096-dm-ubuntuCurrent Portal:,1Persistent Portal: Iface Name: eth0Iface Transport: tcpIface Initiatorname: IPaddress: HWaddress: (null)Iface Netdev: eth0SID: 1iSCSI Connection State: LOGGED INiSCSI Session State: LOGGED INInternal iscsid Session State: NO CHANGECurrent Portal:,1Persistent Portal: Iface Name: eth1Iface Transport: tcpIface Initiatorname: IPaddress: HWaddress: (null)Iface Netdev: eth1SID: 2iSCSI Connection State: LOGGED INiSCSI Session State: LOGGED INInternal iscsid Session State: NO CHANGENotice the two IP addresses in blue above. These are the IP addresses for the two network datainterfaces in my Dell EqualLogic array.8.Issue with making LUN login persistentI noticed that the initiator wasn’t logging in to the LUN automatically after restarting the openiscsi service or rebooting the server, despite having changed the ‘node.startup’ parameter in/etc/iscsi/iscsid.conf to 'automatic'. I looked around and came across this bug: source/open-iscsi/ bug/1001535After looking at the startup script /etc/init.d/open-iscsi, I applied the patch mentioned there andthat fixed it (you can download the patch I used here). When I look in /etc/iscsi/nodes/*/*/, I seethe two iSCSI interfaces I created in step 4, but I don’t see a ‘default’ interface:# ls –l /etc/iscsi/nodes/*/*total 8-rw------- 1 root root 1671 Aug 16 10:16 eth0-rw------- 1 root root 1671 Aug 16 10:16 eth1Verify auto login:# service open-iscsi restart* Disconnecting iSCSI targets[ OK ]9

Dell IncSetting up iSCSI Multipath in Ubuntu Server 12.04* Stopping iSCSI initiator service* Starting iSCSI initiator service iscsid* Setting up iSCSI targets[ OK ][ OK ][ OK ]# iscsiadm –m sessiontcp: [1],1 e9dc2d52096-dm-ubuntutcp: [2],1 e9dc2d52096-dm-ubuntuWe are currently working with Canonical to get clarification on this issue and what the properresolution should be, but the applied patch appears to work well with Ubuntu Server 12.04.4. Setting up MultipathNow that the iSCSI connections are established through both network ports, we are ready to proceedwith setting up multipath.1.Install required package# apt-get install multipath-tools2.Set up configuration file /etc/multipath.conf. There are a myriad of configuration options. TheUbuntu documentation indicates you can leave it empty and use the defaults. Below are theoptions that worked for me, along with a brief comment for each one, Most default options willprobably be ok, but it is highly recommend you read the documentation (man page formultipath.conf) to decide which options are right for you:defaults {user friendly namesyes# Use ‘mpathn’ names for multipath devicespath grouping policymultibus# Place all paths in one priority grouppath checkerreadsector0# Method to determine the state of a pathpolling interval3# How often (in seconds) to poll state of pathspath selector"round-robin 0"# Algorithm to determine what path to use for next I/O operationfailbackimmediate# Failback to highest priority path group with active pathsfeatures"0"no path retry1# These two options go hand-in-hand. The documentation states that# the only value available for ‘feature’ is ‘1 queue if no path’# which is the same as setting no path retry to ‘queue’. However# after trying different values for both, this is what worked for me.# Refer to the multipath.conf man page for details.}blacklist {# devnode " sd[a] "# I highly recommend you blacklist by wwid instead of device name10

Dell IncSetting up iSCSI Multipath in Ubuntu Server ths {multipath {wwid368b7b2dcb6a6af059620d5c29d3e2f7f# alias here can be anything descriptive for your LUNaliasmylun}}To get the WWID of a storage device to either blacklist (i.e. local drive) or to specify an alias for aniSCSI LUN, use the following:# /lib/udev/scsi id --whitelisted --device /dev/sdXWhere X is your storage device name; for example sda is usually a local drive, whereas the iSCSILUN might be sdb and sdc.3.Detect the paths to your iSCSI LUN. If the following command doesn't print anything after running,verify your iSCSI connections:# multipath -v2mylun (368b7b2dcb6a6af059620d5c29d3e2f7f) dm-2 EQLOGIC,100E-00size 60G features '0' hwhandler '0' wp undef - - policy 'round-robin 0' prio 1 status undef - 3:0:0:0 sdb 8:16 undef ready running - 4:0:0:0 sdc 8:32 undef ready runningDisplay multipath topology:# multipath -llmylun (368b7b2dcb6a6af059620d5c29d3e2f7f) dm-2 EQLOGIC,100E-00size 60G features '1 queue if no path' hwhandler '0' wp rw - - policy 'round-robin 0' prio 1 status active - 7:0:0:0 sdb 8:16 active ready running - 8:0:0:0 sdc 8:32 active ready runningThis command will print the name of your multipath device(s), something like mpath0 or in thiscase, the alias ‘mylun’ defined in /etc/multipath.conf. As you can see, there are 2 paths going tothe iSCSI LUN, both of which are active and running.4.Tweak iSCSI failover properties to your liking. The only value I changed (by choice) was thetimeout value for when the operating system will fail over to the other path after one of the twopaths fails. The default value is 120 seconds, which I changed to 10 seconds. I changed it using theiscsiadm command, as setting it in /etc/iscsi/iscsid.conf somehow did not take effect.Display current value (you see the value listed twice since you are connected to the LUN fromtwo paths, but remember it’s the same LUN):# iscsiadm -m node -T e9dc2d52096-dm-ubuntu grep node.session.timeo.replacement timeoutnode.session.timeo.replacement timeout 12011

Dell IncSetting up iSCSI Multipath in Ubuntu Server 12.04node.session.timeo.replacement timeout 120Update value:# iscsiadm -m node -T e9dc2d52096-dm-ubuntu -o update -nnode.session.timeo.replacement timeout -v 10Display new value:# iscsiadm -m node -T e9dc2d52096-dm-ubuntu grep node.session.timeo.replacement timeoutnode.session.timeo.replacement timeout 10node.session.timeo.replacement timeout 105.The iSCSI multipath setup is complete. If you mount a file system on the iSCSI LUN, don’t forgetto pass the netdev option when you mount it. This parameter tells the operating system thatthis is a network file system, so that on a reboot it unmounts it before the network services arestopped. Otherwise, your system will hang on a reboot.To add an entry in /etc/fstab, you would use something like:/dev/mapper/mylun/shareext4netdev0 05. Testing path failoverBefore you are ready to deploy your new iSCSI multipath environment, it’s a good idea to do somesanity checking by simulating a network failure and verifying that the path to the iSCSI LUN is notinterrupted.1.We create an ext4 file system on the iSCSI LUN, mount it on directory /share and then do somedisk I/O on it by using a script to continually create dummy files in that directory:# mkfs.ext4 /dev/mapper/mylun# mkdir /share# mount –o netdev /dev/mapper/mylun /shareHere’s the script I used:#!/bin/bashinterval 1while true; dots date " %Y.%m.%d-%H:%M:%S" echo ts /share/file- {ts}echo "/share/file- {ts}.waiting interval second(s)"sleep intervaldoneThe script creates a dummy file every second and echoes a message to the console. The filename and the echoed message include a time stamp down to the second, so you can easily verifyif there was an interruption writing to the LUN.12

Dell IncSetting up iSCSI Multipath in Ubuntu Server 12.042.Run the script and then simulate a network port failure by unplugging the cable from either oneof the network ports. After 5 seconds, you will see an error message on the screen (and in/var/log/syslog) from the iSCSI subsystem that one of the iSCSI connections has failed. This isnormal and it makes sense since indeed one of the connections has been severed. However, themultipath connection should remain active and the script should continue writing to the iSCSILUN. Verify multipath status:# multipath –llmylun (368b7b2dcb6a6af059620d5c29d3e2f7f) dm-2 EQLOGIC,100E-00size 60G features '1 queue if no path' hwhandler '0' wp rw - - policy 'round-robin 0' prio 1 status active - 4:0:0:0 sdc 8:32 active ready running - 3:0:0:0 sdb 8:16 failed faulty runningIs the script still running? Are files still being written to /share? The answer should be ‘Yes’ for both.3.Plug the network cable back in, wait a few seconds and then unplug the other network cable.Keep looking at the console for messages. You will again see the message from the iSCSIsubsystem about a failed connection, but again, this is normal. Check the multipath status:# multipath –llmylun (368b7b2dcb6a6af059620d5c29d3e2f7f) dm-2 EQLOGIC,100E-00size 60G features '1 queue if no path' hwhandler '0' wp rw - - policy 'round-robin 0' prio 1 status active - 4:0:0:0 sdc 8:32 failed faulty running - 3:0:0:0 sdb 8:16 active ready runningAgain, one of the two paths has failed (although now is the other one). However, the path to theLUN remains active.4.Connect the network cable back in and verify the multipath device. Everything should be back tonormal.# multipath –llmylun (368b7b2dcb6a6af059620d5c29d3e2f7f) dm-2 EQLOGIC,100E-00size 60G features '1 queue if no path' hwhandler '0' wp rw - - policy 'round-robin 0' prio 1 status active - 4:0:0:0 sdc 8:32 active ready running - 3:0:0:0 sdb 8:16 active ready running6. ConclusionSetting up iSCSI Multipath with Dell EqualLogic storage is not drastically different than other enterpriseLinux operating systems. There were a couple of workarounds, but as you can see mostimplementation steps are the same.Please note that the multipath configuration settings in /etc/multipath.conf and the ISCSI timeoutvalues I used here were sufficient for me and will most likely be sufficient for you too, but be sure youfully understand all options available before you deploy your environment.13

Setting up iSCSI Multipath in Ubuntu Server 12.04 7 # sysctl -p 3. Setting up iSCSI connections Before we setup multipathing, we must first establish the iSCSI connection to the LUN. In order to walk you through the iSCSI configuration process, we will illustrate with an example using the same steps that I used in my lab. 1. Install required .

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