iSCSI Configuration

Citrix
Audience
Public
Technology Integrations
Citrix
Source Type
Documentation

Note:

For general iSCSI and SAN Configuration recommendations, please see: SAN Guidelines for Maximizing Pure Performance

Following are the steps for iSCSI configuration:

  1. The best practice recommendations for configuring iSCSI are to use two switches and configure them to be on different subnets. An example is shown below: Notice how the individual NICs are configured to be in different subnets and the corresponding target port IP addresses. This is a mandatory step to make multipathing work correctly. This means we need two switches to be on two subnets.
    Note:

    As of Purity 4.6.0, we do support VLANs. And as of Purity 5.2, we support LACP as well. Also note that Citrix XenServer doesn’t let you do bonding and multipathing, so if you plan to use an existing bond that won’t work with Everpure FlashArray.

  2. Enable jumbo frames (i.e. set MTU to 9000) end to end. At the XenServer initiator ports, switch ports, and the FlashArray target ports.
  3. With XenServer, you can either have bonds or multipathing (MP) but not both at the same time. We prefer to use MP and hence recommend using individual NICs to configure MP on them. This may pose a challenge when we co-exist with other iSCSI vendor arrays. In those cases, it is advised to use additional NICs to configure MP and isolate the network.
  4. We recommend that you update your /etc/multipath.conf file with the settings above in Multipath Configuration. To verify the status, run multipath –ll or multipath status
  5. Additionally, we could set these parameters for higher throughput (bandwidth):
    1. node.session.cmds_max to 1024 (from 128)
    2. node.session.queue_depth to 128 (from 32)
    3. iscsi.MaxRecvDataSegmentLength to 256k (128k is default)
      A reboot is required to make the tunables stick.
  6. Perform the above steps 1-5 on all the hosts in the resource pool.
  7. Obtain the IQN from the XenServer host:
    1. In the XenCenter resource panel, select the host.
    2. Click on the General tab.
    3. Right-click on the iSCSI IQN and make a copy.
    4. If you want to change the iSCSI IQN follow these simple steps:
      1. Select the XenServer host on the XenCenter resource pane.
      2. Click on the General tab.
      3. Click on Properties.
      4. In the dialog, windows make the right changes (for ex. I would change the iqn.2015-02.com.example.my:optional-string to iqn.2015-02.com.pure-xserv-host-01:optional-string)
    5. Use this IQN to do the masking during Pure Storage host configuration.
  8. Configure the SR by right-clicking on the pool and selecting New SR. Add SR with all the IP addresses (target IP of the Pure Storage FA). For example, add all the target port IPs: 10.10.1.10,10.10.2.20,10.10.1.11,10.10.2.21 Select the first one from the Discovery LUN list. However, due to a limitation of Xen Server, only the first IP will be searched but all the paths to that lUN should show up in the Discovery list. Do not choose the wildcard option when only using 1 array as this was not recommend by the Citrix team. The only exception to this is when using AC. The wildcard should only be used when searching LUNs in Active Cluster, as the search will find all paths to that stretched volume.
  9. Make sure you enable multipathing as shown in FC Configuration section (3) for each host.