SSD and USB 3.0 Slower than HDD and USB2.0?

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SSD and USB 3.0 Slower than HDD and USB2.0?

Unread postby Molorius » Tue Feb 06, 2018 6:00 am

I have been contemplating buying an XU4 along with the USB3.0 to SATA Bridge for a server I'm running. I would buy an SSD for this, and I'm more interested in read speeds than write speeds. However, I did a quick test with a Seagate external HDD (from 2015) on my C2, and I'm getting much higher read speeds than Hardkernel's reported numbers with an SSD on the XU4...

My speeds with a C2, external HDD (USB2.0), Ubuntu Minimal provided by Hardkernel (kernel 3.14.79-117):
Code: Select all
dd if=/dev/zero of=test oflag=direct bs=4M count=256
256+0 records in
256+0 records out
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 29.693 s, 36.2 MB/s

dd if=test of=/dev/null iflag=direct bs=4M
256+0 records in
256+0 records out
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 2.63179 s, 408 MB/s


Hardkernel's speed with an XU4 (kernel 4.9.44), USB3.0 to SATA with SSD, taken from http://www.hardkernel.com/main/products/prdt_info.php?g_code=G150462654346:
Code: Select all
dd if=/dev/zero of=test oflag=direct bs=4M count=256
256+0 records in
256+0 records out
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 4.26754 s, 252 MB/s

dd if=test of=/dev/null iflag=direct bs=4M
256+0 records in
256+0 records out
1073741824 bytes (1.1 GB, 1.0 GiB) copied, 4.1119 s, 261 MB/s


Why would the HDD with USB2.0 on the C2 be so much faster with reads than an SSD with USB3.0 on the XU4? I feel like it should definitely be a lot slower, but this small test says otherwise. If that's the case, it appears as though my "upgrade" will actually be worse....
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Re: SSD and USB 3.0 Slower than HDD and USB2.0?

Unread postby odroid » Tue Feb 06, 2018 9:38 am

USB 2.0 maximum throughput can't be higher than 40MB/sec.
"dd" command test result could be wrong due to system caches probably.
Try "iozone" to have a more reliable test result.
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Re: SSD and USB 3.0 Slower than HDD and USB2.0?

Unread postby Molorius » Thu Feb 08, 2018 12:40 am

Whoops, I started a heavy encoding process before looking at this. It will finish in a couple of days, I'll post my results after (for other people to reference). Thanks odroid, I was very confused :D

Now I just need to decide on the XU4 or the N-1.
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languages_spoken: English
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