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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:

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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
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1 Answers1

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The SATA interface runs at 6 Gbps, which due to the 8-bit bytes being encoded into 10-bit symbols with 8b10b line code, equals to 600 MB/s.

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
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