Riverbed Steelfusion – High Latency With IBM Storwize v7000 (BAW12)

As you may recall from previous blog posts, Riverbed Steelfusion is an interesting way to provide the performance of a local VMware environment to a remote office whilst also keeping the data replicated back to a central data centre (or even to a cloud environment).

This is done by presenting out storage from the data centre, via a Steelfusion Core (in the data centre), across your WAN connection to a Steelfusion Edge device.  This storage is then presented as local storage to the virtual environment that is running on the Steelfusion Edge device.  There are other types of configuration for the Steelfusion environment but that then doesn’t have as much appeal, in my eyes.

Anyway, recently we stumbled across a situation where we were seeing extremely large latency (especially with write latency) on the IBM Storwize v7000 storage which was being used for the presented storage in Steelfusion.  When I’m saying extremely high latency, we’re talking about latency figures in the 1000ms range.  This is obviously not good when any data that is modified at the remote office needs to write back to the data centre to be fully committed.  With high latency like this, there is a strong possibility that a lot of this data will not be able to be committed and the amount of uncommitted data will increase.

After investigating this issue with Riverbed, we stumbled onto an issue that had been seen with an Equalogic SAN firmware where uncommitted data would increase significantly.  After careful consideration of the potential impact of the following commands, we implemented them onto two presented LUNs.  To our delight, this resulted in an immediate drop in the latency on those LUNs.  After implementing the changes across all of the LUNs, we were happy to say that the latency returned to a normal level again.

The commands in question need to be run on the Steelfusion Core and need to be run for each presented LUN.  Please note that these commands worked in our environment and are provided for information only.  You should always raise a call with Riverbed or one of their partners to investigate this further before implementing.


To enable the fix (Disable ordered task tag):

storage lun modify serial <lun serial> serialize-write enable


storage lun modify alias <lun alias> serlialize-write enable


To revert the change:

no storage lun modify serial <lun serial> serialize-write enable


no storage lun modify alias <lun alias> serialize-write enable

The link to the Riverbed KB article is here (although you would need to log in to view this):



Blog-a-Week 2018 Posting (BAW):

In previous years, I have had periods throughout the year where I have been unable to post an entry to my blog.  During 2018, my aim is to post a blog entry each week of the year.  I’m hoping that the blog entries will all be useful bits of information or items that I’ve been working on recently but if the standard of the entries drops, I apologise now, as this could have been a busy week and I wasn’t able to put in as much time as I would have liked into the post

About the Author


I have been in IT for the past 15 years and using virtualisation technologies for around the past 8 years. I started, as quite a lot of people do, working with PCs after playing with such iconic systems like the ZX81, ZX Spectrum and then progressing through 386s, 486s, Pentiums etc. After being headhunted at sixth form to work for a small company based around Hertfordshire, UK. I began working with small businesses and gaining a lot of hardware experience. Three years later, after helping to increase the size of the business, I needed to gain exposure to a larger environment to progress my own career. I joined a large manufacturing company around Electronic Test and Measurement which progressed my skills onto more PC work, hardware work and then onto Server Operating Systems. I progressed again onto a consultancy company based in Reading, UK. Initially working as an engineer performing hardware / software installations for larger companies contracted out to the consultancy company, I moved up into a Consultant position continuing my travel across the UK assisting and providing solutions to companies. I finally moved on again to my current position, working back in Hertfordshire, UK. Again working for a large manufacturing company, this time with over 50,000 users worldwide. I am responsible for the datacenter hardware, the storage environment, the vmware environment and also implementing their new Citrix XenApp farm. My days are busy but also productive, its a friendly environment and in my four years of being with the company, I have seen many changes in technology and infrastructure in use within the company. About the site I started this site as I had been thinking of having more of a presence on the web for a while. On a daily basis, I perform tasks and use tools that others may not use or may not think to do and therefore I thought that I would share some of these experiences and tips with others to help with their day to day work. Currently, my main focus of work is around VMware and Veeam Backup & Replication but hopefully as my tasks progress, I’ll be able to share useful bits of information about other areas of IT as well.

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