I’ve a keen interest in SSD, especially SSD based arrays. So I was pretty damn excited when at last weeks HP Discover event in Vienna I saw would could well be the future of SSD and SSD arrays, and it’s cool, really cool…….
Setting the Scene
I’m not a fan of taking a legacy array technologies and shoe-horning them full of SSD. Frankenstorage springs to mind!
I am, however, slightly more of a fan of technologies like Violin Memory and Kaminario (to name just a couple).
However, what I’ve seen at HP Discover has the potential, in my opinion, to make even the likes of todays Violin Memory and Kaminario arrays look legacy, very soon.
Let me take a really quick minute to set the scene…… it wont take long….
In many ways I like Violin Memory. It’s been designed, almost from the ground up with SSD in mind – definitely not a technology designed for rotating rust and then fudged or butchered for SSD. Take the lid off one and you’ll see exactly what I mean.
It looks like a lot of thought and design effort has gone in to it. And the technologist inside of me likes that. However,………. I wonder if it’s too custom and too proprietary to live and thrive in todays market? Todays market demanding commodity and all that jazz!
On the other hand there is Kaminario. These guys take standard off-the-shelf Dell blade systems, off-the-shelf Fusion-io cards, layer some clever software on the top and out pops a high performance SSD array. Ticks the commodity-is-king and software-is-everything checkboxes, but has its drawbacks. Servicing the Fusion-io cards is clunky and requires you to crack the lid of the blade server open (never good in Tier 1 production data centres).
Doing things properly
So what I saw at HP Discover could well be the future of SSD and SSD arrays, and it goes by the name of SCSI Express.
SCSI Express is a protocol that is currently being independently standardised under part of INCITS T10 by the SOP-PQI Working Group and the SCSI Trade Association, with involvement from SFF Committee and PCI-SIG. Quite a crew and quite a project, but it was suggested to me that it might be standardised in six or so months.
SCSI Express enables SCSI over PCIe (SOP), and under the hood it is a SCSI initiator talking to a SCSI target over PCIe via PQI.
PQI stands for PCIe architecture Queueing Interface which is a flexible and extensible transport layer that is very fast and lightweight. I’m told that it leverages the best from some of the existing proprietary SCSI over PCIe solutions available from companies such as PMC, LSI, Marvell and even HP. The difference being that PQI and SCSI Express are being developed as open standards rather than being proprietary to the above mentioned companies. Existing SCSI over PCI protocols such as MPI from PMC are found in silicon in most of the array controllers we see in the world today including EMC, NetApp, Hitachi…
Blah blah blah…. but what does this all mean?
Well, here we have a protocol and interface that is being designed especially for high speed SSD, not spinning rust!
Might not sound much, but when you look at some of the legacy architectures that we are currently bolting SSD drives to (it’s not uncommon to stick an SSD capable of 40,000 IOPs in an array with a backend that can support only a fraction of that) it starts to bring this into perspective. Todays SSD drives are severely hamstrung by the legacy architectures we bolt them to and it verges on a crime to do such.
SCSI Express will release the shackles. It will allow you to take a hot-plug 2.5-inch form factor SSD and install it into a 2.5-inch form factor drive bay on the front of an industry standard server, just like we do with hot-plug drives today. The major difference being that the SSD won’t be hamstrung by SAS or SATA. The drive will mate with a specially designed, but industry standard, interface that will talk a specially designed, but again industry standard, protocol (the protocol enhances the SCSI command set for SSD) with standard drivers that will ship with future versions of major Operating Systems like Windows, Linux and ESXi.
On the topic of hot-pluggable, I’m led to believe that this is not very robust on PCIe as we know it today. However, it’s doable and the guys at HP Discover told me that this should be standardised and available by the time this is productised (somewhere around the end of 2012.
The Future of SSD Arrays
So, again, in my humble opinion, the future of SSD arrays is unlikely to look like a VMAX, VNX or even VSP…… Nor is it going to look like a Violin Memory array.
In my opinion it is going to look like an HP Proliant, Cisco UCS…. name your industry standard off the shelf x86 server, crammed full of industry standard form-factor hot-pluggable SSD drives, running SCSI over PCIe with all of the smarts and clevers in software
on top o VMware (sorry couldn’t resist throwing the VMware comment in).
Seriously though, I can see it. While I love SSD and some of the SSD arrays out there, I’ve has always felt like there is something not quite right about them. I think SCSI Express/SOP is the missing magic!
And when these products ship and change the world, I plan on putting my feet up and retiring, as this will clearly solve every problem that the storage world has or ever will have!
Prototype at HP Discover
The concept box on display at Discover is an early prototype, but was an HP ProLiant server with an early Fusion-io 2.5-inch SSD drive connected to the PCIe bus (I know its not really a bus) via an SFF 8639 backplane connector (PCIe 12Gbps 6 lane). However, this is also doable over PCIe cable implementations.
In the prototype unit at HP Discover, the SCSI Express drives connected to the PCIe bus and bypassed the HP RAID controller similar to the picture below.
This kind of implementation leaves a at least a couple of options when it comes to RAID -
- Have RAID implemented higher up the stack and utilising CPU cycles (the dreaded software RAID).
- develop newer RAID controllers with SCSI Express and SCSI over PCIe in mind
RAID………….. now there’s another technology that could do with being brought in to the 21st Century! but that’s another conversation.
The plug for mating with the server is SFF 8639 and the current board connects to the server via the SAS cables.
Footnote: To SCSI or not to SCSI
Interestingly, the somewhat competing standard of NVM Express is looking to do its magic without SCSI. A bit bolder, but I have to wonder how much harder?
Half of me would love to get rid of SCSI and the legacy that it brings. But then again three quarters of me would have liked to see Ethernet replaced with something like Infiniband. Ethernet clearly isn’t going anywhere and I my head tells me SCSI isn’t either. Too deeply entrenched.
On the positive side though, SCSI is battle hardened and well understood.
Footnote: Competing Standard NVM Express and EMC
No storage futures story is complete without mentioning EMC. Sorry HP and the rest of the storage industry but I like to be honest.
Interestingly EMC are not on the list of companies behind SCSI Express. But they are on the list of those behind NVMe!
As we know, EMC are one of the biggest families in the storage Mafia, and they have significant influence over VMware, one of the biggest families in the technology Mafia. Now, in mind (where 2+2=33) having the daddy of the storage industry behind NVMe, coupled with the interesting noises that VMware has been making about the future of storage, I can’t stop my mind running wild with what they might be up to…. I would it even put it beyond then to be planning the death of SCSI!
Anyway, enough for now. Thoughts and comments mandatory