Upgrading Cisco UCS Fabric Interconnects

I have to do this first, as this is a high-risk change for any environment:

DISCLAMER: I ACCEPT NO RESPONSIBILITY FOR ANY DAMAGE OR CORRUPTION OF DATA THAT MAY OCCUR AS A RESULT OF CARRYING OUT STEPS DESCRIBED BELOW. YOU DO THIS AT YOUR OWN RISK.

And now to the point. Cisco has two generations of Fabric Interconnects with the third generation released just recently. There is 6100 series, which includes 6120XP and 6140XP. Second generation is 6200 series, which introduced unified ports and also has two models in its range – 6248UP and 6296UP. And there is now a third generation of 40Gb fabric interconnects with 6324, 6332 and 6332-16UP models.

We are yet to see mass adoption of 40Gb FIs. And some of the customers are still upgrading from the first to the second generation.

In this blog post we will go through the process of upgrading 6100 fabric interconnects to 6200 by using 6120 and 6248 as an example.

Prerequisites

Cisco UCS has a pair of fabric interconnects which work in an active/passive mode from a control plane perspective. This lets us do an in-place upgrade of a FI cluster by upgrading interconnects one at a time without any further reconfiguration needed in UCS Manager in most cases.

For a successful upgrade old and new interconnects MUST run on the same firmware revision. That means you will need to upgrade the first new FI to the same firmware before you can join it to the cluster to replace the first old FI.

This can be done by booting the FI in a standalone mode, giving it an IP address and installing firmware via UCS Manager.

The second FI won’t need a manual firmware update, because when a FI of the same hardware model is joined to a cluster it’s upgraded automatically from the other FI.

Preparation tasks

It’s a good idea to make a record of all connections from the current fabric interconnects and make a configuration backup before an upgrade.

If you have any unused connections which you’re not planning to move, it’s a good time to disconnect the cables and disable these ports.

Cisco strongly suggests to also upgrade the firmware on all software and hardware components of the existing UCS to the latest recommended version first.

Upgrading firmware on the first new FI

Steps to upgrade firmware on the first new fabric interconnect are as follows:

• Rack and stack the new FI close enough to the old interconnects to make sure all cables can reach it.
• Connect a console cable to the new FI, boot it up and when you are asked “Is this Fabric interconnect part of a cluster”, select NO to boot the FI in a standalone mode.
• Assign an IP address to the FI and connect to it using UCS Manager.
• Upgrade the firmware, which will reboot the fabric interconnect.
• Reset the configuration on the FI, which will cause another reboot:

  • # connect local-mgmt
    # erase config

• Once the FI is upgraded and reset to factory defaults you can proceed with joining it to the cluster.

Replacing the first FI

• Determine which old FI is in the subordinate mode (upgrade a FI only if it’s in subordinate mode!) and disable server ports on it.
• Shut down the old subordinate FI.
• Move L1/L2, management, server and Ethernet/FC/FCoE uplink ports to the new FI.
• Boot the new FI. This time the new FI will detect the presence of the peer FI. When you see the following prompt type YES:

  • Installer has detected the presence of a peer Fabric interconnect. This Fabric interconnect will be added to the cluster. Continue (y/n) ?

• Follow the console prompts and assign an IP address to the new FI. The rest of the settings will be pulled from the peer FI.

Once the new FI joins the cluster you should see the following equipment topology in UCS Manager (This screenshot was made after the primary role had been moved to the new FI. Initially you should see the new FI as subordinate.):

• At this stage make sure that all configuration has been applied to the new FI and you can see all LAN and SAN uplinks and port channels.
• Enable server ports on the new FI and reacknowledge all chassis.

Reacknowledging a chassis might be disruptive to the traffic flow from the blades. So make sure you don’t have any production workloads running on it. If you have two chassis and enough capacity to run all VMs on either of them, you can temporarily move VMs between the chassis and reacknowledge one chassis at a time.

Replacing the second FI

You will need to promote the new FI to be the primary, before proceeding with an upgrade of the second FI. To change the roles, use SSH to log in to the old FI, which is currently the primary (you can’t change roles from the subordinate FI) and run the following commands:

# connect local-mgmt
# cluster lead b
# show cluster state

The rest of the process is exactly the same.

After the upgrade, if needed, reconfigure any of the links which may have had their port numbers changed, such as if you had an expansion module in the old FIs, but not on the new FIs.

References

Cisco has a guide which has a step by step procedures for upgrading fabric interconnects, I/O modules, VIC cards as well as rack-mount servers. Refer to this guide for any further clarifications:

• Upgrading Cisco UCS Hardware

 

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Brocade 300 Firmware Upgrade

In my previous post Brocade 300 Initial Setup I briefly went through the firmware upgrade process, which is a part of every new switch installation. Make sure to check the post out for instructions on how to install a FTP server. You will need it to upload firmware to the switch.

I intentionally didn’t go into all details of firmware upgrade in my previous post, as it’s not necessary for a green field install. For a production switch the process is different. The reason is, if you’re upgrading to a Fabric OS version which is two or more versions apart from the current switch firmware revision, it will be disruptive and take the FC ports offline. Which is fine for a new deployment, but not ideal for production. 

Disruptive and Non-Disruptive Upgrades

Brocade Fabric OS major firmware release versions are 6.3.x, 6.4.x, 7.0.x, 7.1.x, 7.2.x, etc. For a NDU the rule of thumb is to apply all major releases consecutively. For example, if my production FC switch is running FOS version 6.3.2b and I want to upgrade to version 7.2.1d, which is the latest recommended version for my hardware platform, then I’ll have to upgrade from 6.3.2b to 6.4.x to 7.0.x to 7.1.x and finally to 7.2.1d.

First and foremost save the current switch config and make a config backup via FTP (give write permissions to your FTP user’s home folder). Don’t underestimate this step. The last thing you want to do is to recreate all zoning if switch loses config during the upgrade:

> cfgSave
> configUpload

In case you need to restore, you can run the following command to download the backed up config back to the switch:

> configDownload

Next step is to install every firmware revision up to the desired major release (-s key is not required):

> firmwaredownload

Brocade switch has two firmware partitions – primary and secondary. Primary is the partition the switch boots from. And the secondary partition is used for firmware upgrades.

After each upgrade switch does a warm reboot. All FC ports stay up and switch continues to forward FC frames with no disruption to FC traffic. To accomplish that, switch uses the secondary partition to upload the new firmware to and then quickly swap them without disrupting FC switching.

At a high level the upgrade process goes as follows:

• The Fabric OS downloads the firmware to the secondary partition.
• The system performs a high availability reboot (haReboot). After the haReboot, the former secondary partition is the primary partition.
• The system replicates the firmware from the primary to the secondary partition.

Each upgrade may take up to 30 minutes to complete, but in my experience it doesn’t take more than 10 minutes. Once the first switch is upgraded, log back in and check the firmware version. And you will see how secondary partition has now become primary and firmware is uploaded to the secondary partition.

As a last step, check that FC paths on all hosts are active and then move on to the second switch. The steps are exactly the same for each upgrade.

Firmware Upload and Commit

Under normal circumstances when you run the firmwareDownload command, switch does the whole upgrade in an automated fashion. After the upgrade is finished you end up with both primary and secondary partitions on the same firmware version. But if you’re a large enterprise, you may want to test the firmware first and have an option to roll-back.

To accomplish that you can use -s key and disable auto-commit:

Switch will upload the firmware to the secondary partition, switch secondary and primary partitions after a reboot, but won’t replicate the firmware to the secondary partition. You can use the following command to restore firmware back to the previous version:

> firmwareRestore

Or if you’re happy with the firmware, commit it to the secondary partition:

>  firmwareCommit

The only caveat here, a non-disruptive upgrade is not supported in this scenario. When switch reboots, it’ll be disruptive to FC traffic.

Important Notes

When downloading firmware for your switch, make sure to use switch’s vendor web-site. EMC Connectrix DS-300B, Brocade 300 and IBM SAN24B-4 are essentially the same switch, but firmware and supported versions for each OEM vendor may slightly vary. Here are the links where you can get FC switch firmware for some of the vendors:

• EMC: sign in to http://support.emc.com > find your switch model under the product section and go to downloads
• Brocade: sign in to http://www.brocade.com > go to Downloads section > enter FOS in the search field
• Dell: http://www.brocadeassist.com/dellsoftware/public/DELLAssist includes a subset of Fabric OS versions, which are tested and approved by Dell
• IBM: http://ibm.brocadeassist.com/public/FabricOSv6xRelease and http://ibm.brocadeassist.com/public/FabricOSv7xRelease are the links where you can download FOS for IBM switches. You can also go to http://support.ibm.com, search for the switch in the Product Finder and find FOS under the “Downloads (drivers, firmware, PTFs)” section

References

• Brocade Fabric OS 7.x Compatibility Matrix
• Brocade Fabric OS Target Path Selection Guide
• EMC Connectrix B Series Fabric OS Version 7.2.1d Release Notes (can be downloaded from http://support.emc.com)
• EMC Target Revisions and Adoption Rates Report (can be downloaded from http://support.emc.com)

NetApp NVRAM and Write Caching

Overview

NetApp storage systems use several types of memory for data caching. Non-volatile battery-backed memory (NVRAM) is used for write caching (whereas main memory and flash memory in forms of either extension PCIe card or SSD drives is used for read caching). Before going to hard drives all writes are cached in NVRAM. NVRAM memory is split in half and each time 50% of NVRAM gets full, writes are being cached to the second half, while the first half is being written to disks. If during 10 seconds interval NVRAM doesn’t get full, it is forced to flush by a system timer.

To be more precise, when data block comes into NetApp it’s actually written to main memory and then journaled in NVRAM. NVRAM here serves as a backup, in case filer fails. When data has been written to disks as part of so called Consistency Point (CP), write blocks which were cached in main memory become the first target to be evicted and replaced by other data.

Caching Approach

NetApp is frequently criticized for small amounts of write cache. For example FAS3140 has only 512MB of NVRAM, FAS3220 has a bit more 1,6GB. In mirrored HA or MetroCluster configurations NVRAM is mirrored via NVRAM interconnect adapter. Half of the NVRAM is used for local operations and another half for the partner’s. In this case the amount of write cache becomes even smaller. In FAS32xx series NVRAM has been integrated into main memory and is now called NVMEM. You can check the amount of NVRAM/NVMEM in your filer by running:

> sysconfig -a

The are two answers to the question why NetApp includes less cache in their controllers. The first one is given in white paper called “Optimizing Storage Performance and Cost with Intelligent Caching“. It states that NetApp uses different approach to write caching, compared to other vendors. Most often when data block comes in, cache is used to keep the 8KB data block, as well as 8KB inode and 8KB indirect block for large files. This way, write cache can be thought as part of the physical file system, because it mimics its structure. NetApp on the other hand uses journaling approach. When data block is received by the filer, 8KB data block is cached along with 120B header. Header contains all the information needed to replay the operation. After each cache flush Consistency Point (CP) is created, which is a special type of consistent file system snapshot. If controller fails, the only thing which needs to be done is reverting file system to the latest consistency point and replaying the log.

But this white paper was written in 2010. And cache journaling is not a feature unique to NetApp. Many vendors are now using it. The other answer, which makes more sense, was found on one of the toaster mailing list archives here: NVRAM weirdness (UNCLASSIFIED). I’ll just quote the answer:

The reason it’s so small compared to most arrays is because of WAFL. We don’t need that much NVRAM because when writes happen, ONTAP writes out single complete RAID stripes and calculates parity in memory. If there was a need to do lots of reads to regenerate parity, then we’d have to increase the NVRAM more to smooth out performance.

NVLOG Shipping

A feature called NVLOG shipping is an integral part of sync and semi-sync SnapMirror. NVLOG shipping is simply a transfer of NVRAM writes from the primary to a secondary storage system.  Writes on primary cannot be transferred directly to NVRAM of the secondary system, because in contrast to mirrored HA and MetroCluster, SnapMirror doesn’t have any hardware implementation of the NVRAM mirroring. That’s why the stream of data is firstly written to the special files on the volume’s parent aggregate on the secondary system and then are read to the NVRAM.

Documents I found useful:

WP-7107: Optimizing Storage Performance and Cost with Intelligent Caching

TR-3326: 7-Mode SnapMirror Sync and SnapMirror Semi-Sync Overview and Design Considerations

TR-3548: Best Practices for MetroCluster Design and Implementation

United States Patent 7730153: Efficient use of NVRAM during takeover in a node cluster