VSAN VDI Benchmarking and Beta refresh!

I was reading this blog post on VSAN VDI Benchmarking today on Vroom, the VMware Performance blog. You see a lot of people doing synthetic tests (max iops with sequential reads) on all sorts of storage devices, but lately more and more vendors are doing these more “real world performance tests”. While reading this article about VDI benchmarking, and I suggest you check out all parts (part 1, part 2, part 3), there was one thing that stood out to me and that was the comparison between VSAN and an All Flash Array.

The following quotes show the strength of VSAN if you ask me:

we see that VSAN can consolidate 677 heavy users (VDImark) for 7-node and 767 heavy users for 8-node cluster. When compared to the all flash array, we don’t see more than 5% difference in the user consolidation.

Believe me when I say that 5% is not a lot. If you are actively looking at various solutions, I would highly recommend to include the “overhead costs” to your criteria list as depending on the solution chosen this could make a substantial difference. I have seen other solutions requiring a lot more resources. But what about response time, cause that is where the typical All Flash Array shines… ultra low latency, how about VSAN?

Similar to the user consolidation, the response time of Group-A operations in VSAN is similar to what we saw with the all flash array.

Both very interesting results if you ask me. Especially the < 5% in user consolidation is what stood out to me the most! Once again, for more details on these tests read the VDI Benchmarking blog part 1, part 2, part 3!

Beta Refresh

For those who are testing VSAN, there is a BETA refresh available as of today. This release has a fix for the AHCI driver issue… and it increases the disk group limit from 6 to 7. From a disk group perspective this will  come in handy as many servers have 8, 16 or 24 disk slots allowing you to do 7HHDs + 1 SSD per group. Also some additional RVC commands have been added in the storage policy space, I am sure they will come in handy!

Nice side affect of the number of HDDs going up is increase in max capacity:

(8 hosts * (5 diskgroups * 7 HDDs)) * Size of HDD = Total capacity

With 2 TB disks this would result in:

(8 * (5 * 7)) * 2TB = 560TB

Now keep on testing with VSAN and don’t forget to report feedback through the community forums or your VMware rep.

Virtual SAN and maintenance windows…

After writing the article that “4 is the minimum number of hosts for VSAN” I received a lot of questions via email and on twitter etc about the cost associated with it and if this was a must. Let me start with saying that I wrote this article to get people thinking about Sizing their VSAN environment. When it comes to it, Virtual SAN and maintenance windows can be a difficult topic.

I guess there are a couple of things to consider here. Even in a regular storage environment you typically do upgrades in a rolling fashion meaning that if you have two controllers one will be upgraded while they other handles IO. In that case you are also at risk. The thing is though, as a virtualization administrator you have a bit more flexibility, and you expect certain features to work as expected like for instance vSphere HA. You need to ask yourself what is the level of risk I am willing to take, the level of risk I can take?

When it comes to placing a host in to Maintenance Mode, from a VSAN point of view you will need to ask yourself:

  • Do I want to move data from one host to another to maintain availability levels?
  • Do I just want to ensure data accessibility and take the risk of potential downtime during maintenance?

I guess there is something to say for either. When you move data from one node to another, to maintain availability levels, your “maintenance window” could be stretched extremely long. As you would potentially be copying TBs over the network from host to host it could take hours to complete. If your ESXi upgrade including a host reboot takes about 20 minutes, is it acceptable to wait for hours for the data to be migrated? Or do you take the risk, inform your users about the potential downtime, and as such do the maintenance with a higher risk but complete it in minutes rather than hours? After those 20 minutes VSAN would sync up again automatically, so no data loss etc.

It is impossible for me to give you advice on this one to be honest, I would highly recommend to also sit down with your storage team. Look at what their current procedures are today, what they have included in their SLA to the business (if there is one), and how they handle upgrades / periodic maintenance.


Startup News Flash part 9

There we are, part 9 of the Startup News Flash. As mentioned last time, last week was “Storage Field Day” so typically a bit more news then normally this time of year. I would highly recommend to watch the videos. Especially the Coho video is very entertaining.

The original founders of Fusion IO (David Flynn and Rick White) just received 50 Million in funding for their new startup called Primary Data. I mentioned them briefly in Startup News Flash part 3 when they announced they started a new company and it seems that they have something on their hands! They haven’t revealed what they are working on, they are aiming to come out stealth around the second quarter of 2014. In the WSJ the following was mentioned in terms of the space these guys will be playing in: “The company is developing software–though it actually will come bundled on standard server hardware–that essentially connects all those pools of data together, offering what Flynn calls a “unified file directory namespace” visible to all servers in company computer rooms–as well as those “in the cloud” that might be operated by external service companies.” Indeed, something with storage / caching / software defined / scale-out…

I guess scale-out hypervisor based storage solutions are hot… Maxta just officially announced their new product called MxSP. Some rumors had already been floating around but now the details are out their. Marcel v/d Berg did a nice article on them which I recommend reading if you like to get some more details. Basically Maxta created a Virtual Storage Appliance which pools all local storage and presents it as NFS to your hypervisor. Today VMware vSphere is fully supported and KVM / Hyper-V in a limited fashion. It offers functionality like VM-level snapshots and zero-copy clones, Thin provisioning, Inline deduplication and more. It looks like licensing is capacity based but no prices have been mentioned.

When first looking at Avere is was intrigued by their solution but somehow it didn’t really click. Primary focus was a caching layer in between your NFS storage and your hosts… But I wondered why I would want an extra box for that and not just use something host local. Last week Avere made announcement around a solution that allows you to pool local and cloud storage resources and present them via a common namespace and move data between these tiers. FlashCloud is what Avere calls it. Their paper describes it best, so a shameless copy of that: “FlashCloud software running on Avere FXT Edge filers addresses this challenge by storing cold data on cost-effective cloud storage at the core of the network and automatically and efficiently moving active data to the edge near the users.” I like the concept… If you are interested, check out their site here.

Far from a startup, but cool enough to be listed here… The release of the X-Brick aka XtremIO by EMC. The XtremIO solution is a brand new all-flash array which delivers screaming performance in a scale-out fashion. Although there are limitations from a scaling point of view today, it is expected that these will be lifted soon. One of the articles I enjoyed reading is this one by Jason Nash. What is most interesting about the product is the following, and I am going to quote Jason here as he is spot on: “There is no setup and tuning of XtremIO.  No LUNs.  No RAID Groups.  No pools.  No stripe sizes.  No tiering.  Nothing.  You have a pool of very fast storage.  How big do you want that LUN to be?  That’s all you really need to do!”

Another round of funding for SimpliVity, Series C… 58 Million led by Kleiner Perkins Growth Fund and DFJ Growth with contributions by Meritech Capital Partners and Swisscom Ventures. I guess this GigaOM quote says it all: “CEO Doron Kempel, an EMC veteran, said the cash infusion will enable the company to execute on plans to triple its staff and boost sales growth five fold in 2014″.

VSAN performance: many SAS low capacity VS some SATA high capacity?

Something that I have seen popping up multiple times now is the discussion around VSAN and spindles for performance. Someone mentioned on the community forums they were going to buy 20 x 600GB SAS drives for their VSAN environment for each of their 3 hosts. These were 10K SAS disks, which obviously outperform the 7200 RPM SATA drives. I figured I would do some math first:

  • Server with 20 x 600GB 10K SAS = $9,369.99 per host
  • Server with 3 x 4TB Nearline SAS = $4,026.91 per host

So that is about a 4300 dollar difference. Note that I did not spec out the full server, so it was a base model without any additional memory etc, just to illustrate the Perf vs Capacity point. Now as mentioned, of course the 20 spindles would deliver additional performance. Because after all you have additional spindles and better performing spindles. So lets do the math on that one taking some average numbers in to account:

  • 20 x 10K RPM SAS with 140 IOps each = 2800 IOps
  • 3 x 7200 RPM NL-SAS with 80 IOps each = 240 IOps

That is a whopping 2560 IOps difference in total. That does sound like an awe full lot doesn’t it? To  a certain extent it is a lot, but will it really matter in the end? Well the only correct answer here is: it depends.

I mean, if we were talking about a regular RAID based storage system it would be clear straight away… the 20 disks would win for sure. However we are talking VSAN here and VSAN heavily leans on SSD for performance. Meaning that each diskgroup is fronted by an SSD and that SSD is used for both Read Caching (70% of capacity) and write buffering (30%) of capacity. Illustrated in the diagram below.

The real question is what is your expected IO pattern? Will most IO come from read cache? Do you expect a high data change rate and as such could de-staging be problematic when backed by just 3 spindles? Then on top of that, how and when will data be de-staged? I mean, if data sits in write buffer for a while it could be the data changes 3 or 4 times before being destaged, preventing the need to hit the slow spindles. It all depends on your workload, your IO pattern, your particular use case. Looking at the difference in price, I guess it makes sense to ask yourself the question what $ 4300 could buy you?

Well for instance 3 x 400GB Intel S3700 capable of delivering 75k read IOps and 35k write IOps (~800 dollars per SSD). That is extra, as with the server with 20 disks you would also still need to buy SSD and as the rule of thumb is roughly 10% of your disk capacity you can see what either the savings are or the performance benefits could be. In other words, you can double up on the cache without any additional costs compared to the 20-disk server. I guess personally I would try to balance it a bit, I would go for higher capacity drives but probably not all the way up to 4TB. I guess it also depends on the server type you are buying, will they have 2.5″ drive slots or 3.5″? How many drive slots will you have and how many disks will you need to hit the capacity requirements? Are there any other requirements? As this particular user mentioned for instance he expected extremely high sustained IOs and potentially full backups daily, as you can imagine that could impact the number of spindles desired/required to meet performance expectations.

The question remains, what should you do? To be fair, I cannot answer that question for you… I just wanted to show that these are all things one should think about before buying hardware.

Just a nice little fact, today a VSAN host can have 5 Disk Groups with 7 disks, so 35 disks in total. With 32 hosts in a cluster that is 1120 disks… That is some nice capacity right with 4TB disks that are available today.

I also want to point out that a tool is being developed as we speak which will help you making certain decisions around hardware, cache sizing etc. Hopefully more news on that soon,

** Update, as of 26/11/2013 the VSAN Beta Refresh allows for 7 disks in a disk group… **