What an Interface Says About an SSD

When an SSD manufacturer brings a product to market you don’t need to look any further than the interface between the SSD and the server to understand its target market. Solid state storage systems are available with a wide array of sizes, shapes, densities, media, performance, cost and interfaces. The interface used gives the best hints as to how the manufacturer predicted the product would be used and more specifically which market they are targeting.

Fibre Channel SSDs are aimed at the enterprise data center. For most of the last decade, Fibre Channel has been the interface of choice for Tier 1 disk drives and the main interface for attaching external storage arrays in most data centers. Interestingly, the Tier 1 disk drives are now migrating to SAS, but the predominant interface for the enterprise storage array to the server is still Fibre Channel. Companies developing Fibre Channel SSDs want to appeal to enterprise data centers who have made major investments in Fibre Channel based storage area networks. There are plenty of predictions about the demise of Fibre Channel in the data center, but if you were making a choice about an interface for the enterprise today, you would offer Fibre Channel first. If I were deciding the next interface for an SSD or a storage array, I might go with FCOE, but I would probably wait to see that market develop further first. The rapid introduction of converged network adapters (CNA) could translate into changes at the storage controller, but I would also wait to see what happens in that arena.

InfiniBand SSDs are aimed at the high performance computing (HPC) market. InfiniBand is touted for its high bandwidth per link and its low latency. For SSDs with large backplanes, an InfiniBand (IB) controller is a good way to tout your bandwidth capability. Yes, I know there are other companies using IB outside of the HPC market, but the bulk of big opportunities for IB SSD are in that space today. I broadly define HPC to also include oil & gas and entertainment industries. I do believe that IB attached SSDs are an interesting option for data warehousing applications where bandwidth is more important than IOPS.

 NAS SSDs are aimed at the middle of the enterprise. This segment is one of the more intriguing to watch. A couple of companies have made credible attempts to develop NAS caching solutions which sit in front of existing NAS and provide a read or read/write caching layer. In a future blog, I might examine the challenges these companies face. As with mainstream Fibre Channel attached storage, the NAS vendors have incorporated SSD as a storage tier. Only one vendor comes to mind that is doing a pure SSD NAS solution, but others are likely to follow. NAS solutions are so much about software that it is harder for a new company to enter this space and compete with the incumbent suppliers.

iSCSI SSDs are aimed at the low to middle of the enterprise. This has not been a terribly active segment for pure SSD solutions but interesting options are on the horizon. Clearly, existing iSCSI storage arrays have options for including hard disk based SSDs. My automatic expectation when I look at an iSCSI solution is that it will be less expensive than a Fibre Channel SSD. The main reason I would offer iSCSI is to target the cost-sensitive part of the market. Given the increased availability of 10Gbit Ethernet and advanced TCP off-load engines, it is quite reasonable for an iSCSI SSD to offer good performance.

Internal PCI SSD. There has to be an exception to every rule and PCI SSD may be the exception to my rule about an interface telling you about the application for an SSD. PCI SSDs cover a wide variety of price ranges, capacities, media, performance and reliability. On the high end, there are a bunch of applications, particularly scale-out applications, which are server-centric and not storage network centric. PCI SSD have had tremendous success in this category. Similarly, for companies with smaller data sets and budgets, PCI SSD can be alluring. It is not a stretch to pitch PCI SSD for prosumer or high end gaming customers.

External SAS SSD. There are very few externally attached SAS SSDs on the market today. I think the people who offer them were probably temporarily delusional about the future role of SAS in the market and its ability to get rid of Fibre Channel for storage networking. This is not to say that SAS is a bad interconnect, in fact it is being effectively used to replace Fibre Channel as the backplane for many modern storage arrays (i.e. the connections between a disk controller and its enclosures are increasingly SAS).

Hard Disk Drive (HDD) Form Factor SAS SSD.  With the help of solid state storage, SAS HDD has killed the Fibre Channel disk drive. Hard drive form factor SSDs with SAS interfaces are more likely than not intended to be sold to a storage or server OEMs. For the storage OEMs, they replace their Fibre Channel SSDs (if they were ever offered). For the server OEMs, SAS SSD may be used as a boot drive.

SATA SSDs are aimed at the consumer, prosumer, gaming and small business markets. I cannot currently see an enterprise market for SATA SSD. In enterprise storage arrays, SATA HDDs are only used to offer the 3.5” high density (slower) drives.

External PCI. There are a few varieties of external PCI offerings including devices that are ground up designed to offer external PCI SSD and others that are I/O expansion chassis that can be loaded up with PCI SSD. My personal opinion is that the genesis of the external PCI SSD was to serve as extended memory for servers at a time when server memory capacities were limited and at high densities extremely expensive. In my experience, the only way to make one of these devices useful for traditional data centers is to put the external PCI chassis behind some other storage gateway. The storage gateway attaches to the storage network with Fibre Channel. This is all good, but the gateway is now the main dictator of your performance characteristics.

The story on SSD interfaces is certainly not complete. Innovative companies will capitalize on new markets and new interfaces in ways that we cannot yet predict. For the innovators in these segments lie new markets and new opportunities.


2 Responses to What an Interface Says About an SSD

  1. Woody – I agree that interface is a useful shortcut to short listing potential SSD vendors – in many situations.

    Probably the only exception to this is SATA – which encompasses such a large number of SSD suppliers and products – that it’s not the most useful starting point any more – compared with other descriptors such as form factor or intended market (notebook, rugged, enterprise etc).

    You didn’t mention USB. Probably because it’s outside the scope of the enterprise markets you’re involved with.

    USB 3 is the first variant of USB which is usable as a primary SSD connect because it doesn’t waste most of the performance of the attached SSD.

    However – as with all things in the consumer SSD market – the motivation and aspiration of market participants is not always amenable to rational analysis.

    Finally I liked your “delusional” comment re SAS SSDs. Not necessarily because I agree – but it’s probably the first time I’ve seen this type of language in your writing.

    I look forward to your next blog.

  2. […] more… Tags: drive, fibre, fibre-channel, form-factor, hdd, more-likely, regular, sas, solid state hard drives, solid state harddrive, ssd hard drives, the-help […]

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