Archive for VMware

2016 Top Virtualisation Blogs

I’ll keep this post very brief as you can see my thoughts on the subject of soliciting votes for awards in my post from last year!

It’s that time of year again when Eric Siebert of vSphere Land and vLaunchpad runs his annual Top 100 vBlog nominations!

There are a huge number of bloggers around the world producing great documentation and insight, and Eric’s awards give people the opportunity to recognise those who really stand out from the crowd, as well as more up and coming bloggers.

So with that in mind if you’re reading this now, I would encourage you to head over to Eric’s site below and cast your votes; it only takes take a few seconds of your time to show some appreciation for the time and effort put in by those ladies and gentlemen who worked tirelessly throughout the year to help make all of our jobs that little bit easier.

Let’s be honest – it’s got to be more worthwhile than voting for Trump! 🙂

Top vBlog 2016 (sponsored by VMTurbo)

Click here to vote!

Preview – Open Homelab Project at #LonVMUG – 14th April 2016

So this is just a very brief post to firstly say don’t forget it’s the London VMUG on 14th April 2016, at Tech UK (10 Saint Bride Street, EC4A). There are a load of really interesting sessions coming up, both vendor and community.

For example:

  • We have a keynote from Luca Dell’Oca who provided one of the best non-vendorised vendor sessions I have ever seen at a VMUG (his session title this time sounds like he may be looking to up the ante!)!
  • We have loads of sessions on VSAN including the 6.2 updates (also see the Storage Field Day 9 sessions here for a deep dive on that).
  • We even have a session from the London VMUG leadership team’s “Darth Vader” himself, Simon Gallagher, talking about App Volumes!

It should be an awesome day!

agenda-lonvmug-April-2016.png

The keen eyed among you may also notice that I have a session in the list as well…

If you want to come along and be part of a slightly unique session, never been seen before, never been done before, and will probably never be done again (especially if when all goes pear shaped!), then feel free to come along to the Open Homelab project session I will be attempting to herd / steer / keep on the rails!

I suggested a few months ago to Simon G that we do some roundtable sessions at the London VMUG and volunteered to run some as an experiment. These are my favourite sessions at the UK VMUG as you get a dozen or so people round a table and chew the fat on a specific subject area.

It turns out that we don’t actually have anywhere in our new venue to run this session for a small group, so instead, it’s been converted into a “square table”, i.e. “no table” session in one of the standard rooms instead!

Running a roundtable with a room full of people is certainly going to be a challenge, a bit of an experiment, and worst case scenario it all falls apart and we never do it again! Yay! But, hopefully it will actually be a really worthwhile session, and I plan to share the results here afterwards as kind of a crowdsourced homelab advice tree or something! To be honest with less than two weeks to go I haven’t really figured out the details yet, but rest assured by a week on Thursday, I will at least have the title decided!

planning

Whatever happens it should be interesting! So if you want to share your homelab requirements with the group and get some advice and tips on how to design and build it, or if you want to tell us how awesome your lab is already and why you chose to build it like that, please do come along to the session and join in! 🙂

Register here:
London VMUG Meeting Registration – Thursday, 14th April 2016

Words Mean Things, Apparently – Deduplication Myths Explored

A rose by any other name would smell as sweet?

We might all agree that this is most definitely the case, but in the technology industry we have a problem, and it was highlighted across a number of the sessions we attended at Storage Field Day 9 this week.

Specifically, the use of certain terms to describe technology features, when the specific implementations are very different, and have potentially very different outcomes. This is becoming more and more of a problem across the industry as similar features are being “RFP checkboxed” as the same, when in reality they are not.

For example most of the vendors we saw support deduplication in one form or another, and in many cases there was a significant use of the word “inline”.

What do we mean by “inline deduplication”, and what impact to performance can this have?

One of the other delegates at SFD9, W Curtis Preston, had very strong opinions on this, which I am generally inclined to agree with!

UPDATE 08/04/2016: Curtis has recently published an article detailing his thoughts here.

If a write hits the system and is deduplicated prior to being written to its final non-volatile media, be it flash or disk, then it can generally be considered as inline.

Dedupe-Inline

Inline Deduplication

If deduplication is running in hardware (for example as 3PAR do in their Gen4+ ASIC), the deduplication process has minimal overhead on the system, and by not needing to send all writes to the back end storage it can actually improve performance overall, even under sustained high throughput where it can actually improve it by reducing back end writes.

Most non-inline deduplication would typically be referred to as “post-process”, and as a general rule are either run on a schedule or as a lower priority 24/7 system maintenance task. It can also run immediately after the write has gone to disk. This is still post-process, not inline.

It’s worth noting that any of these post-process methods can potentially have an impact on back-end capacity management, as dumping large quantities of data onto a system can temporarily spike capacity utilisation until the dedupe process has time to work its magic and increase storage efficiency. Not ideal if your storage capacity is approaching critical.

depu

In addition, the block has been written to an NVRAM device which should protect it from power loss etc, but the problem we have is that cache is an expensive and finite resource. As such, by throwing a sustained number of IOs at the system, you end up potentially filling up that cache/NVRAM faster than the IOs can be flushed and deduplicated, which is exacerbated by the fact that post-process dedupe generates yet more IOPS on the back end storage (by as much as 2-3x compared to the original write!). The cumulative effect causes IO to back up in the system like a dodgy toilet, thereby increasing latency and reducing your maximum capable IOPS from the system.

Worse still, in some vendor implementations, when system performance is maxed out deduplication in the IO path is dropped altogether, and inbound data is dumped out to disk as fast as possible. Then is then post-processed later, but this could obviously leave you in a bit of a hole again if you are at high capacity utilisation.

Dedupe-post

Post-Process Deduplication

None of this is likely to kick in for the vast majority of customers as they will probably have workloads generating tens of thousands of IOPS, or maybe low hundreds of thousands on aggregate. As such, for most modern systems and mixed workloads, this is unlikely to be a huge problem. However, when you have a use case which is pushing your array or HCI solution to its maximum capability, this can potentially have a significant impact on performance as described above.

[HCI – yet another misappropriated computing acronym, but I’ll let that one slide for now and move on!]

VMware VSAN Deduplication

In the case of one of one of the vendors we saw, VMware, they joked that because of the fact that they initially write to the caching flash tier prior to deduplication, they spent more time arguing over whether it was valid to call this inline than it took them to actually develop the feature! In their case, they have been open enough not to call it “inline” but instead “nearline”.

In part this is because they are always written to a flash device prior to dedupe, but also because not all of the writes to their caching tier actually get sent to the capacity tier. In fact some may live out their entire existence in an non-deduplicated state in flash cache.

dedupe.png

I applaud VMware for their attempt to avoid jumping on the inline bandwagon, though it would have perhaps been better to use a term which doesn’t already mean something completely different in the context of storage! 🙂

You can catch the full VMware session at the link below – it’s well worth a watch!
VMware Storage Presents at Storage Field Day 9

Further Reading

Some of the other SFD9 delegates and VMware staffers had their own takes on the presentation we saw. Check them out here:

Disclaimer/Disclosure: My flights, accommodation, meals, etc, at Storage Field Day 9 were provided by Tech Field Day, but there was no expectation or request for me to write about any of the vendors products or services and I was not compensated in any way for my time at the event.

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