MacBook Pro and the hot new thing: Paired Storage

One hot topic in storage right now is "paired storage," or the combined use of an HDD (hard disk drive) and SSD (solid-state drive), aka a flash drive. A third-party upgrade kit lets owners of the MacBook Pro give this advanced storage architecture a spin.

Some may confuse paired storage with hybrid hard drive technology that was announced a number of years ago. It's different. The hybrid drive incorporates a flash module inside the HDD mechanism. One the other hand, paired storage uses separate flash and hard disk drives simultaneously. This setup can mitigate the performance hit with using just HDDs and the lower capacities found in higher-performing SSDs.

Storage analysts Coughlin Associates and Objective Analysis last week released a joint report on paired storage: HDDs and Flash Memory:  A Marriage of Convenience. According to the authors' projections, paired storage will be found in 53 percent of desktop computers in 5 years and in 25 percent of notebooks in the same time period. They also predict "fat tablets" that will incorporate paired storage.

Other World Computing offers its OWC Data Doubler kit for the MacBook Pro, which lets owners swap out the optical drive and install either a second hard drive or a SSD. The company also sells the SSDs and HDD upgrades. Users can also create a software RAID array with the drives.

This custom engineered black anodized aluminum bracket with attached PCB circuit board comes ready to mount any 9.5mm tall 2.5" SATA hard disk drive and even Solid State Drives.

Because it's connected to the internal SATA connector, the drives are setup and partitioned with Apple's Disk Utility that comes with Mac OS X.

Currently, there's no special sauce in Mac OS X to support paired storage — yet. It's an obvious target for the future. Of course, just booting from an SSD brings plenty of performance.

I asked Robert Peglar, senior fellow at storage vendor Xiotech Corp. and SNIA board member, about where OS makers (Apple, Microsoft and Linux vendors) might target to boost performance on notebooks.

For example, I wondered if enterprise storage optimization techniques such as Fully Automated Storage Tiering (FAST) and continuous adaptive data placement (CADP) might find their way into notebook paired storage systems.

He suggested that boot-up was the best place to start.

At the consumer level, what is required is a very good sense by the distro vendor of what files are critical — especially files which are read-dominant — to be placed in SSD.  Boot is a good example of read-dominant workload, as files are read into memory in very small chunks — sometimes only 512 bytes at a time due to BIOS compatibility — and either executed (executables) or kept resident (device drivers, library routines, etc.)

Speed of boot is important to many consumers.  Beyond that, during normal operation, system-critical files which are read often are good candidates for SSD usage, and the OS must keep track of which files are 'hot'.

However, FAST and CADP were overkill, Peglar said. But for different reasons. FAST analysis of workload is performed over hours of time and can involve large "slices" of a drive.

Many are under the impression that such techniques are 'automatic' or otherwise 'fast'; in fact, they are anything but, and more geared to tiering 'down' to slower media rather than 'up' to faster media.  In addition, their large granularity (e.g. 1GB) is far too large for useful application at the consumer level.

There are other enterprise techniques, such as CADP, which are much more granular and examine 'hot areas' of HDD usage much more frequently, on the order of seconds, to shift real-time workload to SSD. While this technique is very useful for intelligent storage elements in the enterprise, at the consumer level, these techniques are too sophisticated and would result in excessive CPU usage and put strain on the I/O pathways inside consumer devices. Such devices are far better off to use file-level pinning into SSD based on OS history and knowledge.

Apple doesn't offer a MacBook with both solid-state and hard disk storage. But it does in the Mac Pro. Perhaps we will see some advances in the integration of the two types of storage in an update to Mac OS Lion or the release after.