Home PC users are used to the SATA interface because it is as simple as plugging in the power and data cables and voila, the hard drive is ready to go. We use this interface mainly because this is what motherboard manufacturers have decided, which have only built in SATA connectors for a long time, and if we wanted to use the SAS interface, then we will have to resort to cards from extension (wouldn’t be worth it) with an adapter as they need their own controller just like SATA).
What is the SAS interface?
SAS stands for Serial Attached SCSI, and it is a data transfer interface in serious successor precisely to SCSI, which is in parallel. Although SAS continues to use SCSI commands to interact with devices, it increases speed and allows for quick “hot” plugging and unplugging, without having to shut down or restart the computer.
The first version of this standard appeared at the end of 2003 and was then called SAS 300 because it had a bandwidth of 3 Gbps, slightly increasing the speed of the interface at which this happened. It didn’t take long before the evolution, SAS 600, which offered a speed of 6 Gbps equivalent to the current SATA 3, but in 2015 this interface was improved and reaches 12 Gbit / s
One of its main features, moreover, is that it increases the transfer speed of a system by increasing the number of connected devices, that is, it is able to manage a rate of constant transfer for all connected devices, eliminating the limitation of “only” 16 that have SATA and SCSI.
How are SAS hard drives different from SATA drives?
To begin with, we find substantial physical differences between a SATA drive or connector and a SAS, because as you can see below, the SATA interface has the data and power connectors separated by a hole, while the SAS connector is together although it is separated by a piece of plastic. This is to prevent a SATA cable from being connected to a SAS drive as SATA controllers are not able to handle these drives, and yet the reverse is possible i.e. you can connect SATA drive to SAS interface without problems and the controller will recognize it.
As you can imagine, the SAS interface cable is unified into a single connector for power and data, and this is also a point of differentiation since the SATA controller is integrated into the motherboard, while only the motherboards of the servers have a built-in SAS controller and if we wanted to use SAS drives in a home PC, we had to buy a controller in the form of a PCI expansion card.
By the way, in this case it is the controller itself that powers the hard drive and for this reason they can be used with a single connector instead of having separate data and power as in SATA drives.
On the other hand, and although in the past there were SATA hard drives with more than 7200 rpm of rotation speed on their platters (like the famous Velociraptor which triumphed at the time to be the mechanical hard drives the fastest on the market), in general, they are limited to this speed because the interface does not give more of itself; However, when we talk about SAS drives, the usual thing is that they start at 10,000 RPM, and can go up to 15,000 RPM in some cases.
SAS drives are generally much faster than SATA drives, but also more reliable. Since the interface is capable of operating at twice the bandwidth, its transfer speed is also much higher, but above all its ability to handle input and output requests (IOPS) is much higher. For example, the industry admits that the average value of a SATA drive is 80 IOPS while a 15K (15,000 RPM) SAS drive can have up to 180 IOPS. These are averages based on light and heavy workloads.
Speaking of reliability, we just mentioned that SAS drives are more reliable than SATA drives, and coming back to the topic of averages, the industry accepts that a SATA drive has an MTBF (Mean Time to Failure) of d. ‘approximately 700,000 hours, while the MTBF on a SAS drive reaches 1.2 million hours.
Finally, there are also differences in terms of capacity, where SATA drives clearly prevail. If we are talking about drives in the 3.5 inch format, we have in the market 14 and even 18 TB commercial drives that any consumer (who has money) can access, while the larger capacity SAS drives from the market, even today, are 2TB. Obviously, these drives are designed for the professional environment and to operate in very advanced and complex RAID systems, taking advantage of their higher bandwidth for much workloads. more intense to which they are not subjected in the domestic environment.
Now, to answer the question of whether a SAS drive is better than a SATA drive, the answer is clearly yes, it is much better in terms of performance and reliability. Now, considering their limited capacity, the fact that you need a dedicated controller, and the industry doesn’t sell them much in the commercial environment, it’s definitely not worth worrying about. get one – you’d better keep using it. now.