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CADspeed -- Optimizing Hardware for CAD Software

CAD Workstation Storage, Part 1: The Evolving Tradeoffs Between HDD and SSD

Posted by cadhardware

Dec 6, 2011 3:31:31 PM

Advantages and Disadvantages of HDD versus SSD for CAD Workstations

When it comes to thinking about what should go in our workstations, we — both hardware suppliers and users— too often dwell on the glitzier technology inside, the "speeds and feeds." How many CPU cores or GPU shaders there are, what frequencies they're clocked at, and how many polygons/second or texels/second the GPU can churn through.

But just as often as any of these specs might be the bottleneck in your CAD workflow, so might something far less glamorous, like disk I/O performance. To maximize throughput, for both you and your workstation, all the components in your system need to be up to snuff, even — or in some cases especially — your machine's storage.

And what sort of storage subsystem should CAD professionals be considering today when configuring their workstation? Well, there are two basic choices today, the traditional, tried-and-true spinning-platter hard disk drives and the relatively new solid-state drives (SSDs). Which is right for your machine depends on a few criteria, namely capacity, performance and price.

Hard Disk Drives

Beyond their huge capacities available in mind-boggling pennies per Gigabyte, conventional spinning-platter disk drives offer impressive performance as well. Rotating at 7,200 or 10,000 RPMs (5,400 for some mobiles), today's SATA drivers deliver a peak 3.0 Gbps, enough to satisfy most, though certainly not all, CAD applications. (3.0 Gbps is typical for SATA version 2.0, supported by the vast majority of drives shipping today. In the future SATA version 3 will be closer to 6 Gbps. In either case, sustained usable bandwidth will be less.)

Solid State Drives

By contrast, SSDs, which are comprised not of spinning platters of magnetic media but of an array of SRAM chips, offer bandwidth boosts of around two to three times that of HDDs. The SSD's edge in bandwidth is certainly substantial but not necessarily game-changing for most CAD use, not unless you're frequently fetching and storing lots of big models.

Read Latency

But always remember there are two aspects to storage performance. Most think of bandwidth first, but read latency — the time from when the read is requested to the time when data is first received — can often be the bottleneck. Latency is the more serious performance issue when workloads and workflows mandate many short reads that bounce around between different data structures. And more so than bandwidth, it's in the context of latency where SSDs truly shine.

Read latencies for HDDs can range from 10's of milliseconds (seek and/or rotational delay) to a few seconds if those disks have to be spun up from an idle or power-saving mode. With no disks to rotate and no mechanical read heads to move around, read latencies for SSDs are comparatively trivial.

So the answer's easy then, just outfit your drive bays with SSDs, right? It's not that simple, as the HDDs have their compelling advantages as well, namely cost and capacity. Because while SSD prices per byte have come down a lot, they're still down-right exorbitant compared to their disk-based siblings, in the range of 15 to 20 times more expensive. And while the differences in capacities are not quite as dramatic as that, the HDD has the clear advantage. Where 1.5 TB SATA drives are now commonplace, SSDs today are maxing out at around 160 GB.

My next post will help you sort through the options to find the right one for you.

Author: Alex Herrera

Topics: Workstations, Hardware, Hard Drive, SSD Drive, CAD

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