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Goal

Fix

Applies to:

Goal

 This document provides guidelines for the planning and implementation of TCP/IP CLINKs on a VSM5 subsystem.

Fix

 System Requirements
Table 1 lists the minimum hardware, micro code and host software required to enable a VSM5 to perform
replication using TCP/IP CLINKs.

Chapter 1: CLINK Overview

The VSM can be connected to one or more additional VSMs using ESCON and FICON channels. This

connection is referred to as a CLINK. VSMs are traditionally connected both locally and remotely for the

purpose of both high accessibility and disaster recovery.

CLINKs are managed using the Detached Operator Panel (DOP) in the VSM hardware and the Virtual Tape

Control Software (VTCS) configuration statements. The state of each CLINK is controlled by the VTCS using

the VARY CLINK command. This command toggles the CLINK online or offline. The current state of the

CLINK can be viewed using the DISPLAY CLINK command.

Two new capabilities that support IP Replication have been added to VSM5 with the introduction of Enterprise

Library Software (ELS) 7.0:

        Extended Clustering - VTCS supports as many as 14 CLINK definitions per physical VSM attachment,

and more than one VSM can be attached to a single VSM.

        CrossTapePlex Replication - allows replication between Host Software Component (HSC) TapePlexes.

Channel Attached CLINKs

When two VSMs are attached using a channel CLINK on an ICE or VCF interface card, one VSM is designated

as the sender by configuring the connection using a Nearlink Interface and one or more VSMs are designated

as the receiver by configuring the connection using the Host Interface (see Illustration 1). One or two channel

switches or directors can be placed in the connection between the VSMs. These switches or directors can have

extender capability so that the VSM pair can physically reside in different geographical locations.

Channel attached CLINKs require a dedicated channel port on both VSMs. This port may not be shared with

a host or Online Real Tape Drive (RTD) connection.

TCP/IP Attached CLINKs

TCP/IP attached CLINKs perform the same function as channel attached CLINKs, but the TCP/IP connection

exists on the IFF3 interface card instead of the ICE or VCF channel interface card. The TCP/IP connection is

a standard copper Ethernet connector and must be attached either directly to another IFF3 card or a 1 Gb

port on an Ethernet switch. Connections at less than 1 Gb cannot perform replication. When configuring an

IP attached CLINK, the sender port is configured using the Target IP address of the receiver VSM(s). The

host port is configured using the IFF3 Interface card IP address. Refer to the VSM4 and VSM5 Update

Guide for detailed directions configuring IFF3 card addresses and targets. Illustration 2 shows two Local

Area Networks (LAN) connected using a Wide Area Network (WAN). Typically, the LAN is administered by

the datacenter and the WAN is either administered by the datacenter, or leased from a provider.

Chapter 2: Planning and Configuring VSM5 TCP/IP CLINKs

This chapter discusses planning and configuration requirements for VSM5 TCP/IP CLINKs.

Network Equipment Requirements

The TCP/IP CLINK solution does not require any specific network equipment manufacturer, however, our inhouse

testing was performed using Cisco and Dell switches and routers. Any quality switch/router

combination which supports the requirements listed in this section can be used. For best performance from

your VSM5 IP CLINK configuration, ensure the IP network contains the following:

➢ Switches with no more that two 1 Gb ports per ASIC. Connections at less than 1 Gb cannot

perform replication.

➢ Bandwidth of 40 Mb sustained data rate for each VSM5 TCP/IP connection (max 4 physical

connections per VSM5).

➢ Jumbo Frames set to 9000 MTU on the complete path, end to end.

➢ PMTUD enabled on all equipment that does not have a Jumbo MTU of 9000 or greater enabled.

Failure to have PMTUD enabled may result in successful link validations from the VSM5 DOP,

but replication failures when initiated via VTCS. The reason for this is due to DOP Validation

using a very small frame byte size below the standard 1500 MTU.

In some cases Jumbo frames are not feasible on the WAN or LAN due to provider limitations. If Jumbo

frames are not available:

➢ configure the WAN entry router with PMTUD enabled and a Jumbo Frame MTU equal to the

maximum MTU available on the WAN.

➢ configure the LAN entry router with PMTUD enabled and the Jumbo Frame MTU equal to the

maximum MTU on the LAN.

Network Configuration

Perform the following steps to configure your network.

1. Run a path validation tool of your choice to verify frame size, end to end before attempting to

replicate. Verify that a 9000 Jumbo Frame will reach the other end point. For example,

ping -l 9000 xx.xx.xx.xx

2. If packet filtering is enabled, allow the following packets:

     TCP

     TMCP

     ACK

     TCP Keep Alive

3. Enable the “Well Known” ports as follows:

     Control connection port is 50100 plus the number of Targets used (a target is one of four

that exist on a single IFF3 card), e.g., 50000, 50001, ..., 50007

      Data connection port is 50200 plus the number of Targets used, e.g., 50200, 50201, ...,

50207

4. Enable the following “Ephemeral” ports:

      32768 – 65534

Acceptable Network Degradation Levels

      Dropped packets verified to 0.01% packet loss without replication loss

      Jitter verified to 0.11 ms without replication loss

      Duplicate packets tolerated

VSM Configuration

The Sender and Receiver VSMs connect directly to an IP switch using a copper RJ-45 connector. The switch

port used for this connection must be able to negotiate 1Gb line speed. Before connecting the VSM to your

network, perform the following steps. Note that some of these steps may have been performed at the factory

depending upon the manufacture date of your VSM5 subsystem.

1. Check that you are using the proper Ethernet cables:

      CAT5 cables and below are not acceptable for GigE transmission from a VSM

      CAT5E 90m if run through a patch panel, 100m if straight cable

     CAT6 100m regardless of patch panel configuration

2. If your VSM5 has a serial number greater than GUAD:567000200151and BUDA:567000300061,

skip to Step 3, otherwise you are required to enable the 6 MAC address feature. This step is

disruptive because you must Control Power Down (CPD) the VSM and Initial Machine Load

(IML) the VSM in VIP mode. See the VSM4 and VSM5 Update Guide for the complete

procedure.

NOTE: If IFF3 cards are to be installed, then install the IFF3 cards and delete FRUs before starting

the final IML out of VIP.

3. Ensure four IFF3 cards are installed. If not, replace IFF2 cards with IFF3 cards using Guided

FRU Replacement (GFR). Skip this step if it was performed in Step 2.

4. Obtain the IPCluster feature key, then install it from the DOP System and Configuration panel.

Note that you may also need to obtain and enter the ClusteredVTSS feature key if clustering

was not enabled previously.

5. From the IFF3 IP Configuration DOP panel, enter the IP address, Gateway address, and Subnet

mask for each IFF3 interface card.

6. From the IFF3 IP Configuration DOP panel, enter the required Target Addresses.

➢ Each target address may be a different address or the same address. Each address

may be on one or more VSMs depending upon the VTCS software level and CLINK

configuration statements. ELS 7.0 supports multiple VSM connected to a single VSM

and 6.2 and below do not support the multiple VSM to 1 VSM feature set.

➢ A single IFF3 Interface card can service up to 8 incoming targets, however each IFF3

card has a total bandwidth of 40 Mb shared between all targets. The benefit here is the

ability to have the connection defined and offline until needed or to create a more “level”

and “sustained” transmission rate without large peaks and valleys.

Changing an IP Address on the IFF3 Card

Use the following procedure when changing an IP address on a VSM5 IFF3 card from the DOP:

1. Zero any Target fields on other VSM5s that reference the IP address to be changed.

2. On the IFF3 card being modified, zero the IP Address, Default Gateway and Subnet Mask.

3. Enter in this order, the new Subnet Mask, Default Gateway and IP Address.

4. Update the associated Target fields on the receiver VSM5(s).

5. Validate Targets. Note that in some cases it may take multiple validation attempts before the

validation is successful due to network conditions. If the validation is unsuccessful after 2

minutes, check your connections and redo steps 1 through 5.

VTCS Configuration

VTCS requires CLINK statements be defined in its Configuration Control Statements dataset. See the

appropriate VTCS documentation listed in the Bibliography for syntax specifics. The basic steps

required to configure VTCS are as follows:

1. Add a CLINK statement for each IFF3 target configured on your VSM5.

2. Run the VTCS SWSADMIN program with the config dataset as input. See the appropriate

VTCS documentation listed in the Bibliography for details about running a VTCS configuration.

3. Ensure your Management class and Tape Req statements specify replication and are active.

4. Use the Display CLINK command to examine the new CLINK state. They should come online

automatically after a new configuration. If they don't come online, look for error messages or

use the Vary CLINK command to manually vary the new CLINKs online.

5. Test your IP CLINKs by submitting a test job that will create a scratch Virtual Tape Volume (VTV)

and replicate it.

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