HDD speed under SATA I 1.5Gbps

Hi, I'm kind of shocked about the results of an HDD I happen to have which is SATA I 1.5Gbps. I've read that the real maximum speed using this standard is about 150MB/s. Knowing that a HDD has between 70-100MB/s maximum speed, then the SATA I is more than enough to support its maximum speeds if you use a USB 3.0 port.

By the way, I'm using the PC in my signature: Z390, i5-9600K and SSD EVO 850. So everything greatly exceeds the HDD.

However, all I'm achieving is 29-32MB/s, in both sequential read and write, and I don't get it. I'm using a SATA III to USB 3.0 adapter, plugged into a USB 3.0. With other HDDs I get what I'm supposed: 80-90MB/s.

Why is the HDD limited to 30MB/s???
It's as if it was a USB 2.0 interface instead of a SATA I 1.5Gbps.

Parallel to this, I'd like to ask as well another question. I have a USB 3.0 HDD case to transform an internal HDD into an external HDD. It's been working great for many months, andI basically transfer 10-15GB files. As every HDD I've had, the very first seconds there's a burst speed of about 150-300MB/s (which by the way I don't understand how is possible). Then it stabilizes at the known 80-90MB/s and stays there.

Anyways, last week I noticed that when transferring these same sized files, suddenly the first 30-50s I get a speed of 8-15MB/s and then it goes to 60-70MB/s. What the hell is going on?

Both HDD by the way give no warnings or errors in CrystalDiskInfo and have been fully formatted, and the partition table is GPT.

"However, all I'm achieving is 29-32MB/s, in both sequential read and write, and I don't get it. I'm using a SATA III to USB 3.0 adapter, plugged into a USB 3.0. With other HDDs I get what I'm supposed: 80-90MB/s."

USB is a multifunctional interface, so not optimised for the task of file/disc transfers like SATA, and you are using an adapter.
A factor of 2 or so, no surprise.

" As every HDD I've had, the very first seconds there's a burst speed of about 150-300MB/s (which by the way I don't understand how is possible). Then it stabilizes at the known 80-90MB/s and stays there."

All HDDs have a buffer memory which even outs the flow of data to the actual drive itself. At the start that buffer will fill apparently making it look faster in an initial burst. That is filling the buffer rather than writing to the disk itself.

rambomhtri said:

Hi, I'm kind of shocked about the results of an HDD I happen to have which is SATA I 1.5Gbps. I've read that the real maximum speed using this standard is about 150MB/s. Knowing that a HDD has between 70-100MB/s maximum speed, then the SATA I is more than enough to support its maximum speeds if you use a USB 3.0 port.

SATA 1 is 150MB/s (Max communication speed)
HDD has between 40-180MB/s (Max disk read speed)
USB 3.0 port = 4800Mb/s or 600MB/s
USB 2.0 port = 480Mb/s or 60MB/s
By the way, I'm using the PC in my signature: Z390, i5-9600K and SSD EVO 850. So everything greatly exceeds the HDD.

However, all I'm achieving is 29-32MB/s, in both sequential read and write, and I don't get it. I'm using a SATA III to USB 3.0 adapter, plugged into a USB 3.0. With other HDDs I get what I'm supposed: 80-90MB/s.
Why is the HDD limited to 30MB/s???
Old disks are very low speed even if the communication channel is 150MB/s It's as if it was a USB 2.0 interface instead of a SATA I 1.5Gbps.
It is the disk not the communication channel. USB2.0 = 60MB/s
Parallel to this, I'd like to ask as well another question. I have a USB 3.0 HDD case to transform an internal HDD into an external HDD. It's been working great for many months, and I basically transfer 10-15GB files. As every HDD I've had, the very first seconds there's a burst speed of about 150-300MB/s (which by the way I don't understand how is possible). Then it stabilizes at the known 80-90MB/s and stays there.
The fist seconds you transfer from a read buffer to a write buffer. It is transferring from RAM memory to RAM memory. On the sequence it will transfer from the write buffer to the disk (low speed)
Anyways, last week I noticed that when transferring these same sized files, suddenly the first 30-50s I get a speed of 8-15MB/s and then it goes to 60-70MB/s. What the hell is going on?
Depends on the file size and the antivirus that scans every file.

Both HDD by the way give no warnings or errors in CrystalDiskInfo and have been fully formatted, and the partition table is GPT.

See simplified answers in red

Helmut said:

"However, all I'm achieving is 29-32MB/s, in both sequential read and write, and I don't get it. I'm using a SATA III to USB 3.0 adapter, plugged into a USB 3.0. With other HDDs I get what I'm supposed: 80-90MB/s."USB is a multifunctional interface, so not optimised for the task of file/disc transfers like SATA, and you are using an adapter.
A factor of 2 or so, no surprise." As every HDD I've had, the very first seconds there's a burst speed of about 150-300MB/s (which by the way I don't understand how is possible). Then it stabilizes at the known 80-90MB/s and stays there."All HDDs have a buffer memory which even outs the flow of data to the actual drive itself. At the start that buffer will fill apparently making it look faster in an initial burst. That is filling the buffer rather than writing to the disk itself.

What are you talking about?
Of course it is surprising. Any good quality USB 3.0 to SATA adapter will work flawlessly with a SATA HDD, as I have stated here. You will achieve the typical 80-90MB/s stable speed most HDD are capable of.

This is the very first time I see an HDD stuck at 30MB/s using an USB 3.0 adapter. All the rest of the HDD, ALL of them, I've tried over the years, reach the 80-90MB/s in seq. write or read.

I'm pretty sure I've used/tested very old laptop HDDs, like 60GB HDDs, and all of them, under USB 3.0 adapter, give you those 80-90MB/s.

- - - Updated - - -

Megahertz said:

See simplified answers in red

That is the only option I can think of, yes, that the HDD is simply slow. I gotta say this is the very first time I see an HDD this slow, I've never ever seen an HDD perform below 60-70MB/s in seq writing/reading, assuming you are using a USB 3.0 adapter, and I've tested billions of them.

That USB 2.0 speed is not real, the actual speed you will get with a USB 2.0 is about 30MB/s, period. With USB 3.0 you can go up to 300MB/s or so, period.

About the sudden decrease in speed and weird behavior of my USB 3.0 enclosure, I was saying that it was going as expected until last week: as every single HDD, first few seconds burst speed of 300MB/s, and then stable 80-90MB/s, sequential of course. So, I don't know what are you talking about file sizes and antivirus...

You'll be lucky to get 40 MB/s, like an early-2000s 7K HDD. (with USB 2.0)