Posts Tagged ‘standby’

Force10 MXL Switch: Stacking

March 3, 2015

Overview

There are two typical scenarios for stacking MXL’s – within the chassis and across the chassis. In both cases it’s recommended to use ring topology. Daisy chaining is also supported, but not desirable because of the lack of redundancy.

In this post I will be describing the more common case, which is intra-stacking. For inter-stacking configuration you can refer to Dell or Force10 documentation.

Cabling

dell_chassis

In my case I have four MXL switches in bays A1, B1, B2, A2. Cabling is simple, you basically daisy chain all switches and then plug the last switch to the first one.

Stack roles and unit numbers

When stack is built each switch is assigned an ID starting 0 and a role in the stack. There are three roles: Master, Standby and Member:

  • Master – is the switch you’ll use for all configuration. If you currently have IPs assigned to all your MXL switches, all of them except for one will be reset and only the Master will be accessible via SSH.
  • Standby – is the switch which takes over if Master switch fails. Master switch IP address is transferred to Standby in a failover scenario and stack continues to be managed via the same IP.
  • Member switch provides port capacity and doesn’t play any additional roles in the stack.

When you plug cables in, assign stack ports and restart the switches, they will go through election process and automatically pick up roles, as well as IDs. There’s an algorithm that assigns stack IDs and roles, which switches follow. But this algorithm has nothing to do with interconnect bay IDs in the chassis or order in which you cable the switches. You end up with pretty much random numbering.

If order matters, then you’ll have to reboot switches one by one in a particular order to have the desired IDs assigned. In that case IDs are assigned sequentially in a controlled fashion.

Stack configuration

If you don’t have any additional 40GbE modules in slots 0 and 1, then you’ll end up with two QSFP+ ports in a built-in module – ports 33 and 37 (refer to my Force10 MXL Switch: Port Numbering post for port numbering details). All you need to do is to designate them as stack ports on all switches, save config and reboot.

# stack-unit 0 stack-group 0
# stack-unit 0 stack-group 1
# copy run start
# reload

By default each switch is unit 0 in its own stack and stack-group is basically just a 40GbE stack port. You can have maximum of six such ports numbered from 0 to 5. To check that stack ports have been enabled run:

# do show system stack-unit 0 stack-group configured

enabled_ports

It could be that your 40GbE ports are in quad 10GbE mode and are not shown. You’ll need to convert them back to 40GbE mode to proceed. To show the list of available ports type in the command below. Switch shows empty expansion slots as stack ports as well (port 0/41 and 0/45), which is a bit confusing.

# show system stack-unit 0 stack-group

port_list

After a reboot, switches will join the stack and get a role and an id. This process is automatic by default. To see if stack ports have come up after a reboot type:

# show system stack-port status

stack_up

Conclusion

In my example I let switches to go through election process and select roles and IDs on their own. If you want to control the assignment process refer to Dell and Force10 documentation for instructions.

Now you may wonder if unit IDs are assigned automatically, how do you know which stack unit corresponds to which chassis bay ID. The hint for that is to show system inventory and map them by the Service Tag ID which is also shown in the Chassis Management Controller:

# show system brief
# show inventory

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Windows MPIO with IBM storage

September 17, 2012

IBM mid-range storage systems (like DS3950) work in active/passive mode. It means that access to each LUN is given through one controller, in constrast to active/active storage where data between host and two controllers can flow in round-robin fashion. So redundant path here is used only as a failover. Software which provides this failover functionality is called Multipath I/O (MPIO) and has implementations for all operating systems. I’ll desribe how to configure MPIO version for Windows.

Installation

Prior to Windows Server 2008, Microsoft didn’t have its own MPIO implementation and MPIO was distributed with IBM DS Storage Manager product. Now you can install MPIO from “Feautures” sub-menu of Windows Server 2008 Server Manager. After installation is complete you will find MPIO configuration options under Control Panel and in Administrative Tools.

IBM storage works well with default Windows MPIO implementation, however it’s recommended to install IBM MPIO (device-specific module) from Storage Manager installation bundle. In my case MPIO installation file was called SMIA-WSX64-01.03.0305.0608.

Enable multipathing

Initially you will see two hard drives for each LUN in Device Manager. You can enable MPIO for particular hardware ID (in other words, storage system) on Discover Multi-Paths tab of MPIO control panel. You can’t do that with LUN granularity. After you add selected devices and reboot, you will see them on “MPIO Devices” tab. Now each LUN will be seen as a single hard drive in Device Manager.

Configure preferred path

MPIO supports several load-balancing policies, which are configured on a LUN basis from MPIO tab of a hard drive in Device Manager. As a Load Balance Policy select Fail Over Only. Then for each path select which is Active/Optimized and which is a Standby path. Also make active path Preferred, so that after failover it failbacks to it.

Don’t be confused by iSCSI on the figure. It’s the same for pure FC. It’s just for reference.

Check configuration

When you configure active and passive paths you assume that first path listed is to controller A and second path is to controller B. But, in fact, there is no indication of that from the configuration page and you can neither confirm nor deny it. The only ID you see is adapter ports but they don’t even map to the actual ports on HBAs.

To be able to check your configuration you need to install IBM SMdevices utility which comes with IBM DS Storage Manager. Run DS SM installation and go for Custom Installation. There you need to check only the Utilities part. In SMdevices output you can see which path is preferred for this LUN and if it’s configured as active (In Use):

C:\Program Files\IBM_DS\util>SMdevices
IBM System Storage DS Storage Manager Devices
. . .
\\.\PHYSICALDRIVE1 [Storage Subsystem ITSO5300, Logical
Drive 1, LUN 0, Logical Drive ID
<600a0b80002904de000005a246d82e17>, Preferred Path
(Controller-A): In Use]

References

The best reference I found on that topic is IBM Midrange System Storage Hardware Guide (SG24-7676-01), from p.453: DS5000 logical drive representation in Windows Server 2008. As well as Installing and Configuring MPIO guide from Microsoft.