Hybrid vs. flash - vSphere Tutorial

- [Rick] In this video, we'll compare and contrast Hybrid versus All-Flash architecture with vSan. And so, we'll start out with the Hybrid vSan configuration. So, in this configuration, we have a flash device and a traditional hard disk device in each disk group. Each disk group can contain one SSD, and anywhere between one and seven traditional magnetic disks. And the purpose of the SSD in this scenario is to provide us with our cache tier. So, the only purpose of the SSD is to improve performance. What we want to do is store our most frequently read data in that SSD, and that way, when a virtual machine performs any sort of read operation, hopefully that read will be satisfied by the SSD in a very fast to low latency manner rather than satisfied by the HDD, rather than be satisfied by the traditional, physical, magnetic spinning disk, which is always slower. So, that's a hybrid configuration. Now, in this configuration, we're saving some money, most likely, because the hard disks are a lot less expensive than SSD and they can store a lot more data. Now, when there is a write operation in a Hybrid vSan model, it is written to the SSD as a write buffer, and at that point, the virtual machine is done with the write operation. vSan later will copy that data from SSD to the hard disks and to our capacity tier. So, that's Hybrid vSan, and you've already learned a little bit about that in a few of the lessons we've gone through. So, why would I choose Hybrid Mode? Number one, it's less expensive. Traditional hard disks are significantly less expensive per gigabyte than SSD, so we can get a lot more capacity at a lower cost. And if you have a workload with a consistent data set, that is ideal. So, what do I mean by that? Well, if the same data is consistently being read, there's a very good chance that that data is going to be read from SSD most of the time. So, if I have a really consistent data set for my virtual machine, the number of times that I actually have a cache miss and need to pull that data from HDD is going to go way down. So, a consistent data set is ideal. It's also great for desktop virtualization because with desktop virtualization, you're often going to use something called linked clones or instant clones. These are virtual desktop solutions that employ a shared disk that is shared by many virtual machines. That's a consistent data set. That's this big chunk of data that a lot of virtual machines are going to access frequently, and so the majority of that data is going to end up in our SSD and is going to work really well with desktop virtualization. Okay, so now that we've covered Hybrid Mode, let's look at the alternative, an All-Flash vSan configuration. So, in an All-Flash vSan configuration, you see these hard disks here in orange? Those are going to go away, and we're are going to replace them with capacity tier SSD devices. So, there are still two tiers here, just like with Hybrid. Let's go back real quick. Just like with Hybrid, I had my SSD as the cached tier. I had my hard disk drives as the capacity tier. Well, that doesn't actually change with an All-Flash configuration. We're still going to have certain SSDs that are marked as our cache tier in each disk group, and then behind that, anywhere from one to seven capacity devices. So, that model actually doesn't change. So, why doesn't that model change? Well, what we're going to do is we're going to use the SSD as a write buffer. So, the SSD is going to strictly act as a write buffer, and then, the capacity SSDs are going to work the way that they always have, just like our hard disks worked before. So, why do this? Why have one SSD specifically dedicated as a write buffer, and then, anywhere from one to seven capacity SSDs behind it? Well, we're going to spend more money on this cache tier SSD. This SSD is going to handle a whole ton of write operations. It's going to have a lot of concurrent writes going at it. And the other thing that we have to bear in mind is it has to be extremely durable. We don't want this SSD going down. And so, if you look at your different options for SSD storage, some are more durable than others, some are built to basically fail after many writes instead of not so many, and so what we want to do is on that buffer, on that cache tier, we want to choose an enterprise-grade, really fast, very highly durable SSD, and then we can go a little bit cheaper on the capacity tier SSDs. So, it's just a good way for us to kind of, possibly save a little money by going a little bit cheaper on the capacity tier SSDs, but don't do that on the cache tier because, like I said, it's going to handle a whole lot of write operations. So, why would we choose an All-Flash configuration? Well, basically, you're just looking for the fastest possible performance. It's better performing in all use cases, typically somewhere around 50% in performance improvement versus the Hybrid configuration. And the cost for Flash is steadily declining, so as that cost continues to go down, it makes more and more sense. The other big piece of this puzzle is that VMWare is definitely driving towards this direction of an All-Flash configuration, and as part of that effort, they are supporting new features in the All-Flash configuration that are not supported in the Hybrid configuration. Features like RAID 5 and 6 support. So, with RAID 5 and 6 support, what we can do is we can maintain the redundancy and availability of our data, but there's much less overhead. There's much less extra space consumed. So, RAID 5 and 6 can save us a lot of space, so can de-duplication and compression, and these are all things that are supported on an All-Flash configuration but are not supported in Hybrid Mode. So, in review, Hybrid Mode is less expensive, Hybrid Mode gives us more capacity, whereas All-Flash is most expensive, but it gives us better performance. And the price is continuously coming down, not only because SSDs are getting cheaper, but VMWare is introducing space saving techniques like RAID 5, RAID 6, de-duplication, and compression that can reduce the overall cost for an All-Flash configuration.