SAS versus SATA Drives – What is the Difference?

Sata vs Sas

Around 300 million hard drive disks shipped in 2017 alone. That’s without any mention of solid state drives, the main competition for traditional HDDs.

Even within the world of HDDs, you find a divide that many people don’t recognize immediately. Specifically, it’s the SAS vs SATA hard drive divide.

Both SATA and SAS use the traditional platters and magnetic read/write heads people associate with hard drives. That means the drives look very similar on the surface.

In practice, you’ll find more than one difference between SAS and SATA drives. Keep reading and we’ll walk you through some of the big differences.

Cost

Right at the top of the list of differences between SAS and SATA hard drives is the cost.

SAS drives routinely cost more than SATA drives. A decent 300GB SAS hard drive might run you $200-$300. By comparison, you can get a decent 1TB SATA drive for less than $100 dollars.

The price difference isn’t price gouging on the part of hard drive manufacturers. SAS and SATA drives offer very different kinds of performance across several areas.

Errors

One of the main differences between SAS and SATA drives is the rate of unrecoverable read errors (URE). In basic terms, a URE happens when a hard drive finds a spot that it can’t read and the drive fails.

Without delving into numbers that don’t mean much to most people, SAS drives experience these failures far less often. The difference in error rates typically gets expressed in orders of magnitude. So, for example, a SAS drive might prove 10 times or 100 times less likely to fail.

The thing you should bear in mind is that error rates are related directly to the amount of data that a drive reads. The more data a drive reads, the more likely a drive will experience errors.

SATA drives generally end up in consumer computers. SAS drives end up in enterprise systems.

Consumer computers process substantially less data on average than enterprise systems. Consumer computer data processing can generally be measured in gigabytes from day-to-day. Enterprise systems routinely process terabytes of data.

Speed and Storage

SAS and SATA operate in largely separate worlds when it comes to speed.

A typical SATA drive averages 7200 rpm. Some SATA drives still show up at 5400 rpm and a small percentage have a higher speed.

SAS drives average either 10,000 rpm or 15,000 rpm. Those higher speeds let SAS drives read and write faster than SATA drives.

SAS drives typically show better data transfer numbers than SATA drives. SATA drives generally max out around 600 MB/s. SAS drives max out around 1500 MB/s.

An important point of note is that SAS drives get built with speed as the goal. SATA drives get built with storage as the goal. That goal difference helps explain the rpm and data transfer discrepancies.

It also explains why most SAS drives offer 1TB or less of storage. You can easily find 4TB and 6TB SATA hard drives.

Reliability

The standard measurement that manufacturers use for drive reliability is “mean time between failures” (MTBF). It’s a frustrating number for most consumers because it’s usually given in hundreds of thousands of hours.

Manufacturers come up with this number by testing a bunch of drives for a defined period of time and seeing how many fail. They use those numbers to calculate the general MTBF for that drive.

The MTBF might not give you much information about the useful life you’ll get out of a single drive. What it does offer is a good general comparison about how SATA drives stack up against SAS drives.

MTBF for SATA drives maxes out around 1.2 million hours, with most coming in well below that. Most SAS drive MTBFs start around 1.2 million hours and go up from there.

Temperature also affects overall reliability. SATA drives work best around room temperature. If the temperature goes up, reliability goes down.

SAS drives remain reliable up to temperatures around 110 degrees Fahrenheit. This is another reason they end up in enterprise systems.

Server rooms, for example, often run quite hot even with a dedicated cooling system in place. SATA drives would fail far more often in that kind of environment.

Uses

For all intents and purposes, SATA and SAS drives serve entirely different groups of customers.

Consumer-grade computers use SATA drives as the standard. This happens in part because the drives are cheaper. That helps keep consumer grade hardware at reasonable price points.

It’s also because typical consumers don’t require their computers to perform demanding work 24/7 for years on end. For example, you might edit photos or stream videos for several hours on your computer. Then, you stop and turn your computer off for the night.

Corporations and data centers use SAS drives in their servers. They require drives that can withstand 24/7 use, provide extra speed, and have fewer errors.

For example, say a company sells retail products online through their website.

They need that website available at all times. They also need any customer data they collect to stay intact over time. If their drives failed all the time, data corruption would happen on a regular basis.

They could lose order information or entire customer accounts.

Take a web hosting company as an example. Their entire business depends on the drives in their servers working consistently at all times. If their drives fail, they literally can’t provide the service their business is based on.

Parting Thoughts on SAS vs SATA Drives

In terms of SAS vs SATA, there are very real differences.

SAS drives offer better speeds, fewer errors, and more reliability. SATA drives provide a better price and more storage.

They also serve very different customer groups. SATA drives end up in consumer-grade computers while SAS drives end up in enterprise servers.

The lower performance specs of SATA drives rarely make a difference in the consumer computing experience. The better performance specs of SAS drives make a tremendous difference for companies that need reliable drives that can operate 24/7.

VRLA Tech specializes in custom-built workstations and servers. For more information about our custom hardware, contact us today.

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