The Promise of Solid State Disks

Technology: Page (1) of 1 - 09/17/04

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The Promise of Solid State Disks By John Virata

Traditional Winchester technology has long been the standard storage technology used for not only the personal computer, but for editing systems as well. On the plus side, disk drives are used in the industry because they are cheap, fast, and they get the job done. On the minus side, they are prone to failure, wiping out all your data as well as the time you spent editing that data. So, when another technology comes around in an attempt to challenge the leader in storage technology, people can tend to become skeptical.

It has happened before. When Steve Jobs formed NExT Computer, the computer systems were built around Magneto-optical drives, and not traditional Winchester drives. It didn't catch on. Magneto-Optical drive technology was touted by many companies as the next great storage medium. It too has become more of a footnote in the history of storage technology. Now Solid State Disk (SSD) technology seems to be making a run at becoming a viable storage alternative to the lowly Winchester-based hard disk drive. The main issue that proponents of SSDs seem to focus on with regard to Winchester based technology is the speed, or lack thereof, that traditional hard disk drives output as a part of the overall storage solution. They see the hard disk drive as the bottleneck for data transfer by virtue of its design; Data is stored on a disk platter that spins at a certain speed, and the magnetic head, which retrieves that data must move back and forth to find the data, read it, and write it. In addition, the traditional Winchester drives are more prone to physical damage due to shock, vibrations, or severe temperature swings. Solid State Drives, on the other hand are built around DRAM modules which obviate the necessity to synchronize a magnetic head with a rotating platter.

Video and HD editing are storage hogs that require huge amounts of bandwidth to keep that data moving. Are Solid State Disks up to the task of moving data in a video editing workflow? To get some answers on the technology, DMN senior editor John B. Virata spoke with Woody Hutsell, executive vice president at SSD manufacturer Texas Memory Systems, one of the first vendors targeting the editing space with SSD drives, and discussed at length, the promise of SSDs, some of the issues that affect the current state of SSD, and what SSD drives can bring to the table in a video editing workflow.

DMN: Video editing is extremely bandwidth intensive. How do you see solid state disks fitting into the realm of digital video and HD editing?

RamSan-320

Woody Hutsell, Texas Memory Systems: Solid state disks, with high bandwidth, are uniquely able to support work models where multiple editors need to edit shared high definition content. For example, a single Texas Memory Systems RamSan-320 solid state disk can deliver over 1.5GB per second of sustained random bandwidth through its eight 2Gbit fibre channel ports. Paired with a good SAN shared file system, this capability can be shared across multiple servers. A weakness of solid state disks is that their capacity per unit is insufficient for most content. Therefore, as with hard disk drives, it is necessary to array the solid state disks.

Arrays of solid state disk can offer unreal performance, but carry relatively steep price tags. A product that we think will be more relevant to the mainstream non-linear video editing market is our RamSan-330 external fibre channel cache. This system sits transparently in front of other external fibre channel RAID systems and automatically caches data passing from servers to RAID. The benefit of this external fibre channel cache is that it can be flexibly deployed to support a single LUN within a RAID or even support multiple RAID units. Non-linear video editing applications tend to be fairly cache friendly. In other words, if one user is already editing certain content, then that content will be in cache. Therefore, the second editor will be editing from the cache thus improving performance.

DMN: Today, most editors are still using traditional hard disk drives in their pipelines because hard disk drives work. Have the vendors of editing systems been receptive to SSD drives as viable to that of traditional hard disk drives?
WH: Solid state disks are definitely a viable solution, the challenge is figuring out how to flexibly deploy solid state disks so that you can manage hardware costs. In certain environments, capacity requirements are not as big of a problem (such as editors for commercials) or where a solid state disk can be used to accelerate metadata accesses for SAN shared file systems. In cases where the capacity requirements are in the terabytes, solid state disks are frequently considered but are usually determined to be too expensive. We believe our RamSan-330 external fibre channel cache offers the best solution for this market as it allows a company to use performance where it is needed and cheaper RAID systems for content storage. As the price for memory continues to decrease and as content bandwidth requirements increase, solid state disks could easily become a required solution.

DMN: Do you see storage based on solid state disks replacing traditional Winchester-based technology?
WH: This is fairly unlikely for the near future (five to ten years). The main issue is cost. There is some big percentage of applications that can get good performance from hard disk drives. This combined with the higher cost of solid state storage, makes it unlikely that solid state disks will be the future of storage. The reality is that the future will hold ever increasing amounts of cache and solid state storage because the technologies have so much to offer from a price:performance point of view.

DMN: What is the maximum storage capacity of SSD drives?
WH: Our RamSan-320 solid state disk and RamSan-330 external fibre channel cache units each hold from 16-64GB in a single unit. We are working on doubling this density in our next product release. As mentioned earlier, the systems can be arrayed for larger capacities. For example, our largest customer implementation is 2.5 terabytes (40 of our RamSan-320 units).

DMN: What are the benefits that SSDs possess over that of Winchester technology?
WH: 1. 250x lower latency for data accesses.
2. Better performance with random data accesses. For example, our systems can handle over 1.5GB per second of sustained random data access. It would take racks full of RAID to reach this performance level with random data. Similarly, the units excel at high I/O rates. For example, our RamSan-320 can provide over 250,000 random IOPS.
3. Better price/performance. The best way to understand this is to look at storageperformance.org, the website for the Storage Performance Council. Texas Memory Systems completed testing with the SPC-1 specification which mimics an OLTP environment. In this testing, which is audited by the Council, Texas Memory Systems has the world record for SPC-1 IOPS and the world record for SPC-1 IOPS/dollar. In other words, our solution is the fastest and the best price for performance of all of the results submitted to the Council.

DMN: What kind of bandwidth benefits do SSDs have over hard drives?
WH: This is a tricky question, mostly because it depends as much on the architecture of the solid state disk or hard drive system as it does with the underlying media. Keep in mind that most hard disk drive manufacturers and RAID manufacturers quote their bandwidth numbers in terms of sequential data access. This is kind of cheating as there are few applications that use data sequentially. A single editor working on HD content is likely just streaming data from the disk drive. Multiple editors result in random data accesses to the storage, which is a big reason RAID units perform so poorly in this configuration. A single hard disk drive might be able to stream data at around 50-60MB/second (under the proper optimal conditions). A single RamSan-320 can move data at over 1.5GB per second (even with random data). In contrast, the Apple X-Serve RAID publishes peak bandwidth at around 352MB/second sustained throughput (a number that is definitely based on sequential data accesses). Finally, there are some solid state disks that can only handle 100MB/second.

DMN: How does backup work with a SSD solution?
WH: Because a solid state disk is just like a disk drive to the operating system, any current backup methods can be used with a solid state disk just like they could with a hard disk drive. A key issue customers are concerned about is how we handle the volatility of the memory system. Both our solid state disk and caching solution include three RAID-3 protected hard disk drives and three batteries. The batteries power the system for up to thirty minutes after external power fails. We will use that time to dump data from the memory to the internal hard disk drives. These mechanisms are in place to promote non-volatility and do not replace the need for good backup software.

DMN: Because SSDs are built primarily of DRAM modules, wouldn't SSDs be more prone to price fluctuations?
WH: The volatility of the DDR RAM prices definitely makes it more difficult for SSD vendors to price their products. For example, we have kept our prices steady over the last year even as DDR RAM prices have increased 20%. Generally speaking, you can count on memory prices going down over the long term, it is just over the short term that memory price volatility can cause problems.

DMN: What about costs? Hard disk drives have come down exponentially in cost, from $3000 for a 3GB drive 10 years ago to under one dollar a gigabyte today. How much more is it to implement an SSD solution in a storage pipeline?
WH: There is still a big disparity in cost/capacity between hard disk drives and solid state disks. While our prices have come down at least as rapidly as hard disk drive prices, they are still much higher. For example, it is possible to buy 73GB hard disk drives for under $100 (depending on interface technology). This same capacity in solid state disks will still cost you nearly $100,000. If cost/capacity was the only consideration, solid state disks would never be implemented. It is in situations where price/performance is more important that cost/capacity that solid state disks are selected. Solid state disks are also often the only solution to some tough I/O bottlenecks.

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John Virata is senior editor of Digital Media Online. You can email him at jvirata@digitalmedianet.com

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