SATA 3 hard drives have a maximum theoretical transfer speed of 6 Gb/s or 600 MB/s. However, real-world speeds are lower due to overhead. Actual transfer speeds for SATA 3 hard drives range from around 450-550 MB/s for sequential reads/writes.
What is SATA?
SATA stands for Serial Advanced Technology Attachment. It is an interface used to connect storage devices like hard drives and SSDs to a computer’s motherboard.
SATA was designed to replace the older Parallel ATA (PATA) standard and has gone through several revisions:
- SATA 1.0 – 1.5 Gb/s or 150 MB/s (released in 2003)
- SATA 2.0 – 3 Gb/s or 300 MB/s (released in 2004)
- SATA 3.0 – 6 Gb/s or 600 MB/s (released in 2009)
SATA 3.0 is the fastest and newest generation of SATA interfaces. It is also referred to as SATA III or SATA 6Gb/s. Most modern hard drives use the SATA 3.0 interface to connect to computers.
SATA 3.0 Interface Speed
The SATA 3.0 interface has a maximum theoretical transfer speed of 6 Gb/s or 600 MB/s. This is the total bandwidth capacity of the interface connection.
However, the actual transfer speed of a SATA 3 hard drive is lower due to overhead. Overhead refers to additional communication and processing that must occur along with the actual data transfer.
Some key factors that contribute to overhead and lower real-world SATA 3 speeds include:
- Command processing – The drive must receive, interpret and respond to commands sent over SATA
- Error checking – Additional data is transmitted for error checking and correction
- Encryption – Encryption/decryption processes if drive uses encrypted storage
- File system data – File tables, indexes and other file system metadata must be read/written
- Host bus adapter – The SATA controller chip also uses some SATA bandwidth
Due to this overhead, maximum speeds are only achieved during sequential file transfers in ideal conditions. The overhead has a larger impact on small random file transfers.
Real-World SATA 3.0 Hard Drive Speeds
While the SATA 3.0 interface has a theoretical limit of 600 MB/s, current hard drive technology is unable to reach those speeds. Actual real-world SATA 3 hard drive speeds depend on factors like:
- Drive rotation speed (RPM)
- Cache size
- Density of data on the platters
- Controller and interface chipset
Based on these factors, most SATA 3 hard drives have max speeds of 450-550 MB/s.
Sequential Read/Write Speeds
For sequential reads and writes of large files, SATA 3 hard drives can reach speeds of ~450-550 MB/s. This includes activities like:
- Copying large files between drives
- Reading/writing large files like videos
- Backing up drive contents
Top-end SATA 3 hard drives may reach over 550 MB/s for sequential transfers. For example, the Seagate Barracuda Pro 10TB drive claims speeds up to 560 MB/s for sequential reads and writes.
Random Access Speeds
For small random file transfers, SATA 3 HDDs have much lower speeds, usually in the 0.5 – 1.5 ms per random read/write range. This includes things like:
- Loading applications
- Boot up times
- Random access of small files
So while SATA 3 HDDs can match the ~500 MB/s speeds of the interface for sequential file transfers, their random access performance is still bottlenecked by the physical limitations of HDD technology.
SATA 3 vs SATA 2 Speed Differences
Upgrading from a SATA 2 to SATA 3 hard drive can provide a noticeable boost in transfer speeds in some cases. For example:
- A SATA 2 hard drive may reach sequential speeds of only 300 MB/s due to the SATA 2 interface limit of 300 MB/s
- The same drive upgraded to SATA 3 could reach ~500 MB/s since the SATA 3 interface maximum is 600 MB/s
However, there are cases when a SATA 2 and SATA 3 hard drive will have very similar real-world speeds. This happens when the hard drive itself can’t saturate the SATA 2 bandwidth.
For example, a 5400 RPM SATA 2 hard drive may only achieve 120 MB/s transfers. The same slow drive upgraded to SATA 3 would still only achieve ~120 MB/s since that is its limit based on the drive technology.
So upgrading to SATA 3 only helps maximize transfer speeds if the hard drive technology itself is fast enough to benefit from the extra bandwidth. Top end SATA 2 drives around 300 MB/s can see a nice bump from upgrading to SATA 3 and a faster ~500 MB/s bandwidth.
SATA 3.0 RAID Performance
Using multiple SATA 3.0 hard drives in a performance RAID setup can provide increased bandwidth that surpasses single hard drive speeds.
Some examples of transfer speed improvements:
- RAID 0 – Data is striped across drives for increased bandwidth. A 2 drive RAID 0 array can achieve ~900 MB/s.
- RAID 5 – Parity data is distributed across drives for redundancy. A 3 drive RAID 5 array can provide ~750 MB/s.
- RAID 10 – Combines mirroring and striping for performance and redundancy. A 4 drive RAID 10 array can reach ~1000 MB/s.
However, the downside of RAID is increased cost since multiple hard drives are needed. Also, RAID levels like RAID 0 increase speed but provide no data redundancy.
Overall, SATA 3.0 RAID arrays can deliver substantial performance gains over a single hard drive, provided the workload can take advantage of the increased sequential read/write bandwidth.
SATA 3.0 vs NVMe SSD Speeds
While SATA 3.0 hard drives are fast compared to previous HDD interfaces, Solid State Drives (SSDs) connected via PCIe NVMe blow away SATA 3.0 HDDs:
- Top SATA 3 HDD Speed: ~550 MB/s
- NVMe Gen3 x4 SSD Speed: ~3,500 MB/s
This huge performance gap is why NVMe SSDs are the preferred choice in modern PCs over SATA SSDs and HDDs. The NVMe interface provides massive bandwidth of up to 4 GB/s per lane which allows NVMe SSDs to reach their full potential.
SATA 3.0 is still fine for cheaper bulk storage, but for primary storage NVMe SSDs are far superior in terms of bandwidth, latency, power efficiency and scalability.
Real-World SATA 3.0 Hard Drive Examples
To give an idea of real-world SATA 3.0 hard drive performance, here are some examples across different drive types:
5400 RPM Hard Drive
- WD Blue 1TB 5400 RPM Hard Drive
- 128MB Cache
- Up to 180 MB/s sustained transfer rate
As an example of a slow, energy efficient hard drive. Performance is limited by the low spindle speed despite the SATA 3.0 interface.
7200 RPM Hard Drive
- Seagate Barracuda 2TB 7200 RPM Hard Drive
- 256MB Cache
- Up to 210 MB/s sustained transfer rate
A typical mainstream desktop hard drive. The faster 7200 RPM spindle speed improves performance over 5400 RPM drives. But still limited versus higher end models.
High Performance 7200 RPM Hard Drive
- WD Black 6TB 7200 RPM Hard Drive
- 128MB Cache
- Up to 261 MB/s sustained transfer rate
Example of a top performing 7200 RPM hard drive. Takes advantage of the SATA 3.0 interface with faster platter density and caching.
10,000 RPM Enterprise Hard Drive
- Seagate Savvio 10K.7 600GB 10,000 RPM Hard Drive
- 64MB Cache
- Up to 477 MB/s sustained transfer rate
Top-end enterprise class hard drive designed for performance. The extremely fast 10,000 RPM spindle speed allows it fully take advantage of SATA 3.0 bandwidth.
SATA 3.0 – Fine for Mainstream, Not High Performance
In summary, SATA 3.0 hard drives provide adequate performance for mainstream desktops and storage. Maximum speeds of ~500 MB/s are sufficient for general usage. Enterprise workloads may utilize specialized high RPM SATA 3.0 drives.
However, for high performance applications, NVMe solid state drives are far superior. NVMe delivers up to 6x higher bandwidth along with lower latency and power efficiency benefits. The future is NVMe SSDs, while SATA 3.0 hard drives serve well as bulk storage.