Tweaking the Hybrid Drive Model

SSDs and hard disk drives excel in different aspects of the storage equation, so it really wasn't a surprise when Seagate decided to put the two together.

By Arthur Cole | Posted Jan 5, 2011
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SSDs and hard disk drives excel in different aspects of the storage equation. On one side, you have low power consumption and high throughput -- on the other, there is bulk storage at low cost.

So it really wasn't a surprise when creative minds at Seagate decided to put the two together peanut-butter-cup-style to see if two great tastes really do taste great together. It turns out they did, which is why the Momentus XT hybrid drive helped propel Seagate into the SSD realm long after the first enterprise-class drives had hit the channel.

The Momentus XT provides up to 750 GB of hard disk storage with 4 GB of SSD storage, which is typically used as a cache for the most frequently accessed data. In this way, you really do get the capacity and speed benefits of both technologies.

Very soon, however, the ability to adjust both cache and bulk storage capacity will be upon us. Marvell just introduced the HyperDUO SATA controller chip that essentially allows you to mix and match any hard drive and SSD you like. The SoC is already slated for the newest ASRock, Asus, Gigabyte and MSI motherboards, as well as Micron SSDs and Seagate and Western Digital HDDs. The device uses a technique known as "automated tiering," which seeks out popular files and mirrors them to an associated SSD, which not only improves performance but protects against data loss as well.

Another hybrid solution that's gotten little notice outside of laptop circles is the HDDBoost system from Silverstone. For less than $50, you get a small housing with some electronics that accommodates a wide range of SSD configurations and connects them to a standard hard drive and motherboard. The result is a simple RAID 1 device that allows you to cache hard disk data on the SSD. Naturally, performance is based on the drives themselves. Storage Review gave it mostly positive marks, but cautioned that there is no intelligent data mechanism like on the Momentus XT -- only the front end of the HDD capacity gets cached, rather than the most frequently accessed data, so not every application will see faster throughput.

The drawback to all these solutions, however, is that while SSDs are fast, they tend to wear out quickly in high-performance environments. What would be nice is a cache for the cache that can limit the number of writes and rewrites on the SSD. A MacWorld blogger called QuickSander says he came up with a solution for an old iMac that involves storing Safari cache on a RAM drive, which is then only written on logout. I leave it to better minds than mine as to whether something similar could be set up in an enterprise setting, but at least it shows there are multiple ways to tackle a storage problem through creative management.

After the first rush of enterprise-class SSDs was over and talk of the "all-SSD data center" had faded, it became clear that the most effective way to deploy the technology was in conjunction with legacy storage systems. Hybrid drives and RAID configurations certainly make that job easier.

The only question now is where the technology will go from here.

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