5

What is the actual max read/write speed for a SATA III 6.0Gb/s Hard Disk Drive realistically?

I know what 6.0gb/s means, it means six gigabit per second, the giga- prefix uses SI decimal definition, which means 1,000,000,000, and it is 1,000 times a mega- and 1,000,000 times a kilo-, but computers use binary and use Byte as the base unit, 1 Byte = 8 bit, with each unit 1,024 times of the former, so 1 KB is 1,024 Byte and 8,192 bit, 1 MB is 1,048,576 Byte and 8,388,608 bit, and 1 GB is 1,073,741,824 Byte and 8,589,934,592 bit, so 6.0gb/s in decimal would be 732,421.875 KB/s or 715.2557373046875 MB/s in binary.

But in reality, my HDD is Seagate BarraCuda ST1000DM010 1TB 7200 RPM 64MB SATA III 6.0gb/s and connected to a SATA III 6.0gb/s port on my motherboard:

enter image description here

Yet I have never observed disk read/write speed of this HDD higher than 160MiB/s in taskmgr.exe, using FastCopy with a buffer size of 256MiB to copy a files from the same HDD gives a transfer rate of 128MiB/s at most, and typically around 108MiB/s most of the time, interestingly Get-FileHash can spike the I/O speed of the HDD up to 144MiB/s.

So what is the maximum read/write speed of a SATA III HDD at 7200 rpm with SATA 6.0gb/s interface?

I ask this question because I plan to buy Seagate Exos 7E8 4TB 512n SATA 128MB Cache 3.5-Inch Enterprise Hard Drive (ST4000NM0035), it has 128MB cache instead of mine's 64MB, so what read/write speed should I expect? Would it be about 256MiB/s, because it has cache twice the size of mine, or something higher?

So SATA uses 8b/10b encoding so theoretically the max data rate is 4.8gb/s which equals to 600MB/s or 572.20458984375MiB/s, however this speed is way higher than what I am actually able to get...

Ξένη Γήινος
  • 2,824
  • 6
  • 28
  • 62
  • 1
    your observations for Mechanical HDD performance, for a decent 7200RMP disk on SATAIII more or less match mine. if you want to improve the performance substantially you will have to look into SSD. The cache size won't impact your actual speed, just the length of time you can keep at max speed, during sequential R/W. Cache smooths out the bumps, but for continuous usage, it can't even pretend to improve peak read/write speed. – Frank Thomas Mar 13 '21 at 08:49
  • 1
    *"I know what 6.0gb/s means..."* -- There's more to it than a simple conversion from a bits to bytes rate. See https://superuser.com/questions/1432487/data-transfer-rate-query. Also, the SATA interface is but just one sequential operation or transfer in a chain of required operations/transfers to perform a read or write operation. To read or write of a single sector or cluster, these independent operations/transfers must be performed sequentially, one at a time. See https://superuser.com/questions/350582/when-a-disk-read-or-disk-write-occurs-where-does-the-data-go/350592#350592 – sawdust Mar 13 '21 at 09:38
  • *"however this speed is way higher ..."* -- The speed of the interface (in this case, SATA) does not have to match the (internal) speed of the storage device (in this case, a HDD). Both commands and data are transmitted over SATA. You want a fast interface. It's like a trip with one leg is by car and the next leg is by plane. You're complaining that the car is too slow and the plane is too fast. The independent but sequential phases do not require speeds to match. – sawdust Mar 13 '21 at 20:00

1 Answers1

7

The SATA interface runs at 6 GBps.

It is just that a mechanical rotating hard drive cannot achieve such high read or write speeds.

It even reads in the Seagate ST1000DM010 manual what kind of burst and sustained read/write speeds can be achieved. The average is 156 MB/s even if the interface speed is 600 MB/s.

Justme
  • 1,529
  • 1
  • 7
  • 10
  • Stop editing the post with false information. SATA 6Gbps link is **NOT** able to transfer 750 MB/s, it is 600 MB/s due to 8-bit bytes being encoded to 10-bit symbols. – Justme Feb 13 '23 at 06:35