Yellow Bricks

by Duncan Epping

VPLEX Geosynchrony 5.2 supporting up to 10ms latency with HA/DRS

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I was just informed that as of last week VPLEX Metro with Geosynchrony 5.2 has been certified for a round trip (RTT) latency up to 10ms while running HA/DRS in a vMSC solution. So far all vMSC solutions had been certified with 5ms RTT and this is a major breakthrough if you ask me. Great to see that EMC spent the time certifying this including support for HA and DRS across this distance.

Round-trip-time for a non-uniform host access configuration is now supported up to 10 milliseconds for VPLEX Geosynchrony 5.2 and ESXi 5.5 with NMP and PowerPath

More details on this topic can be found here:

Using differently sized disks in a VSAN environment

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Internally someone asked this question, and at the Italian VMUG I had someone asking me the same question… What if I want to scale out, or scale-up, and need to add differently sized disks to my existing VSAN environment? Will that be an as expensive exercise as with (some) traditional RAID systems?

Some of you have introduced new disks to RAID sets in the pasts may have seen this: you add a 2TB disk to a RAID config that only has 1TB disks and you waste 1TB as the RAID set only includes the capacity of the other disks. VSAN is not like this fortunately!

With VSAN you can scale-up and scale-out dynamically. VSAN does not, to a certain extend, care about the disk capacity. For VSAN the disk is just destination to store objects, and there is no filesystem or lower level formatting going on to stripe blocks across the disks, sure it uses a filesystem… but this is “local” to the disk, and not across disks. So whether it is a 1TB disk you add to an environment with all 1TB disks, or you add a 2TB disk, it will not matter to VSAN. Same applies to replacing disks by the way, if you need to replace a 1TB disk because it has gone bad and would like to use a 2TB disk instead… go ahead! Each disk will have its own filesystem, and the full capacity can be used by VSAN!

The question then arises, will it make a difference if I use RAID-0 or Passthrough at the disk controller level? Again, it does not. Keep in mind that when you do RAID-0 configurations for VSAN that each disk is in its own RAID-0 configuration. Meaning that if you have 3 disks, you will have 3 x RAID-0 set each containing 1 disk. Of course, there is a small implication here when you replace disks as you will need to remove the old RAID-0 set with that disk and create a new RAID-0 set with the new disk, but that is fairly straight forward.

One thing to keep in mind though, from an architectural / operational perspective… if you swap out a 1TB disk for a 2TB disk then you will need to ask yourself will this impact the experience for my customers. Will the performance be different? Because 100 IOps coming from the same disk for 1TB is different then 100IOps coming from the same disk for 2TB, as you will (simply said) be sharing the 100IOps with more VMs (capacity). In short: 100 IOps for a 1000GB disk = 0,1 IOps per GB BUT 100 IOps for a 2000GB disk = 0,05 IOps per GB, you can see the potential impact right… You have more capacity per disk, but with the same number of IOps being provided by that disk. Hopefully though the majority of IO (all writes will for sure, and most reads) will be handles by flash so the impact should be relatively low. Still, something to consider.

Virtual Volumes vendor demos

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I was at the Italian VMUG last week and one of the users asked me what Virtual Volumes would look like. He wanted to know if the experience would be similar to the “VM Storage Policy” experiences he has been having with Virtual SAN. I didn’t have an environment running capable of demonstrating Virtual SAN unfortunately so I shared the following videos with him. Considering I already did a blog post on this topic almost 2 years back I figured I would also publicly share these videos. Note that these videos are demos/previews, and no statement is made when or even if this technology will ever be released.

HA restarts in a DR/DA event

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I received a couple of questions last week about HA restarts in the scenario where a full site failure has occurred or a part of the storage system has failed and needs to be taken over by another datacenter. Yes indeed this is related to stretched clusters and HA restarts in a DR/DA event.

The questions were straight forward, how does the restart time-out work and what happens after the last retry? I wrote about HA restarts and the sequence last year, so lets just copy and paste that here:

  • Initial restart attempt
  • If the initial attempt failed, a restart will be retried after 2 minutes of the previous attempt
  • If the previous attempt failed, a restart will be retried after 4 minutes of the previous attempt
  • If the previous attempt failed, a restart will be retried after 8 minutes of the previous attempt
  • If the previous attempt failed, a restart will be retried after 16 minutes of the previous attempt

You can extend the restart retry by increasing the value “das.maxvmrestartcount”. And then after every 15/16 minutes a new restart will be attempted. The question this triggered though is why would it even take 4 retries? The answer I got was: we don’t know if we will be able to fail over the storage within 30 minutes and if we will have sufficient compute resources…

Here comes the sweet part about vSphere HA, it actually is a pretty smart solution, it will know if VMs can be restarted or not. In this case as the datastore is not available there is absolutely no point in even trying and HA as such will not even bother. As soon as the storage becomes available though the restart attempts will start. Same applies to compute resource, if for whatever reason there is insufficient unreserved compute resources to restart your VMs then HA will wait for them to become available… nice right!?! Do note I emphasized the word “unreserved” as that is what HA cares about and not actually about used resources.

Re: SFD5 event and negativity / respect

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Storage Field Day was hosted last week, and I typically like these events. Mainly because they have start-ups presenting their new technology and I like the flow of the sessions typically. I also like the interaction between the “delegates” and the vendors, well at times I do. There were several blog posts on the topic from people who are part of the, what I would call at this point, old boys club (yes there were women attending as well but you get the point) as that is what it felt like during the event. I wanted to comment on Bob’s article, but it looks like he is not looking for a healthy debate so I figured a blog post would be the best way to reply.

For those who don’t know: The sessions usually start with some background on the company, a problem description and then followed by a product session with demos and deep-dives where and when needed. Delegates will fire off questions during these sessions, sometimes this leads to a great discussion and sometimes it doesn’t.

This week, as some of you may have noticed on twitter, the event was held but personally I didn’t enjoy it very much. I think this tweet from my friend Jason Boche captures the feeling I had well:

What stood out to me, and by watching twitter to others as well, was the negativity from some of the delegates about some of the vendors. When the initial problem statement/marketing fluff would take too long the “boring” comments from the delegates started to pass by on twitter, especially during the start of the EMC session this was particularly bad. (Not the first time I have seen it… and definitely not trying to defend a vendor here as they could have known what they were up against and should know the first rule of presenting: know your audience.) Maybe even more annoying for the person watching the feed were the “inside jokes” and the “annecotes” / “incrowd discussions”. It really disrupted the flow of some of the sessions, and I think the PernixData session was the best example of it… it derailed too often leading to the presenter running out of time, or as Frank put it:

https://twitter.com/FrankDenneman/status/459235681345482752

When several people commented on the tweets/atmosphere some heated debates kicked off. What stood out to me during these debates was that the “delegates” felt that they were doing the vendors a service and that the vendors should respect their time/effort. (I agree with them to  a certain extend) It was also mentioned various times that they were all experts and there was no need for basics/problem descriptions as all had done their due diligence and came well prepared. Personally I don’t believe that based on the questions asked, and personally I think everyone can learn something even from the basics, besides that I would argue that the Tech Field Day website is really clear on this:

Don’t assume all of the attendees are experts in your area. True to the spirit of Gestalt IT, we intentionally mix many IT disciplines at Tech Field Day to spark creativity and out-of-the-box thinking.

And on the topic of respect; it goes both ways and it seems that the Tech Field Day charter agrees with me on this as this is what it states in the section what it is like to be a delegate:

… just treat them with the thoughtfulness, professionalism and mutual respect they deserve.

But what is the underlying problem? What the delegates seem to have forgotten is the vendor’s perception… Why are these vendors there. What is their reason to participate? Are they looking for feedback from a handful of people on their product(s) and aiming to make road map changes  when needed… Or are they looking to introduce their product (or new version) to the world through the reach the event has? (note I said event and not delegates on purpose) I would expect it to be the latter, as the majority of companies presenting are presenting a new product or version and not a road map on top of that I would argue that if they are looking for direct product feedback they would do this in a closed setting with a limited group of people under a strict NDA. Even when that would not be the case, just as you are asking the vendor to be respectful of your time, you should also be respectful towards them for what they are investing. Which is probably a lot more than just time as without their sponsorship there would not be an event. (Assuming Mr Stephen Foskett is not a secret billionaire… But who knows :-)) Either way, think about what allows these events to exist. Without these companies investing, it would be difficult for Stephen to organize these. Also, think about the people watching the event online and even about the person sitting next to you. What is glaringly obvious to you, may not be so for the person sitting next to you simply because they come from a different background.

So why am I writing this, well hopefully so things will change for the better. As I stated, I like these events  as they are valuable to the community in my opinion and they provide a nice podium for start-ups to present themselves to the world, but that positive aspect should not get lost in unneeded debates and negativity. As that is what these events are about in my opinion, it is providing a service to the community and I hope it will stay that way.

PS: I have a lot of respect for the endless effort Stephen puts in organizing these sessions / events…