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Servers 101: HDD Interface Comparison – SATA vs SCSI vs SAS

March 11, 2019


Hard drive terminology can be confusing for the uninitiated. SATA vs SCSI vs SAS... it can take months or even years to fully understand what these seemingly random jumbles of letters mean.

Well, we here at ServerMonkey would like to shorten the learning curve with this quick overview of the difference between the various enterprise drive interfaces. If you’re looking for an in-depth discussion on technical specs, this isn’t the place – just call us up anytime and we’ll be happy to nerd out on bus speed, hot-plug capability, and robust tagged command queuing. In the meantime, here’s a quick and dirty overview of the three most popular HDD interfaces to get you started.

What is a SCSI Hard Drive?

SCSI is an acronym for Small Computer System Interface, pronounced “scuzzy”. SCSI hard drives have been the backbone of enterprise computing for nearly 20 years. Though they typically don’t possess much in the way of capacity (the last generation of SCSI drives consisted mostly of 36GB, 73GB, and 146GB models), SCSI drives make up for it with speed.

SCSI drives come in 10,000 or 15,000 rotations per minute (RPM) versions, meaning it will access data much faster than your desktop will (desktop drives are generally 5400 or 7200 RPM). If you have mission-critical applications that aren’t too big but need to be accessed quickly, SCSI is a great choice.

SAS Hard Drive – A Better Choice for Mission Critical Applications

SAS, which stands for Serial Attached SCSI, is basically a beefed-up version of a SCSI drive. For mission-critical applications, an SAS hard drive is the better choice.

SAS drives have higher transfer speeds (3 or 6Gbit/s, as opposed to a maximum of 5120 Mbit/s for SCSI), thinner cables, and are more easily linkable with SATA drives. They also come in more form factors – all SCSI drives are 3.5”, but SAS drives can be 2.5”, allowing for their use in more compact systems.

SAS drives also come in larger capacities (they go up to 600GBs and beyond, whereas SCSI stops at 300GB), while maintaining the 10K and 15K RPM speeds. Naturally, though, the tradeoff is that SAS drives cost more than SCSI ones. Still, for important applications that require real-time access, SAS is the new SCSI.

The SATA Hard Drive

Then there are SATA drives. SATA (or Serial ATA, which stands for Serial Advanced Technology Attachment) is the interface used by most desktop and laptops on the market today.

That doesn’t mean that you can take an HDD out of your old desktop and slot it into a server, though – servers use special Enterprise-class SATA drives that are faster and more reliable. Even so, Enterprise SATA drives are going to be slower than a SCSI or SAS drive, only going up to 7200 RPM.

They make up for this in capacity, however – the current generation of Enterprise SATA drives don’t go much lower than 250GB and can go as high as 2TB.

If you’re looking for drives with a lot of room and don’t want to pay a huge premium for SAS-level speed, an Enterprise SATA hard drive is the way to go.

SATA vs SCSI vs SAS: The Takeaways

It’s no surprise, but different interfaces are good for different things:

  • If you need speed and transfer rate, SCSI is a good choice, and SAS even better.
  • If capacity is your main concern, SATA is a better option.
  • For price, SATA is once again king based on a pure specs-to-cost ratio, though for a mix of speed and cost, SCSI drives can be very affordable as well.

The bottom line though is that hard drive interface is just one choice to make when picking a server. Memory, CPU, number of drive bays, RAID, remote access control, etc. … all these must be factored in, and oftentimes your choices there will dictate your choice of hard drives.

The biggest example of this is compatibility – a server that will take SCSI drives will only take SCSI drives, whereas a server that can take SAS will be able to take SATA drives (with a few exceptions).

Fortunately, ServerMonkey helps you out with this choice by offering you all the best HDD options on every server we offer. Whether you want a low-end SCSI machine or a high-end rackmount full of SAS and SATA drives, ServerMonkey can accommodate you!

If you have any further questions on HDD interface comparisons, contact our experts at 1-855-432-8918 and we’ll be happy to answer all your questions. You can also contact us online at https://www.servermonkey.com/contact.