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Forum Discussion
chadwixk
Dec 31, 2022Aspirant
Copy Speed Test Results to USB 3.0 Drive w/ SSD - why so slow?
NAS: RN102 I need to copy off about 3TB of data...I know not a ton, but was curious to test various copy methods to see which was fastest and just to learn a little more in the process. SOURC...
chadwixk
Dec 31, 2022Aspirant
Thank you StephenB for your time in responding and helping me learn and investigate this.
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I see how to quote you're entire reply, but I don't know how to break up the quote to then insert my replies...curious how if you don't mind...so bear with my formatting below to mimic this...well I could use the raw html editing, but that would take a while...and I'm assuming there is an easier way to do this how you did in your replies
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The slow CPU and limited memory in the RN102 likely is also a factor.
I'm not a hardware or linux guy (more a microsoft web dev), so not sure if I'm interpreting these properly, but CPU and Mem or not at 100%, but maybe they are effectively at 100%, limiting throughput?
Theoretically, yes. But from what I've read (posts on other forums), a single file is only read from one disk. A second file copy should be read from the second disk if it is done at the same time. But this is not something I've tested.
Tried this, one session running RoboCopy and one running cp, IOSTAT still shows a 20MB/s read and write (in this view CPU also does seem to be pegged).
But USB 3.0 is ~600 MB/s, so it would be the write bottleneck. Or possibly the NVME adapter you used???
True, but we're waaaay less than the 600MB/s bottleneck. The NVME adapter is well doing well over 1,000MB/s from Crystal Disk tests.
Did you measure the read and write speeds on the RN102 using dd? Might be worth doing (for both source and destination).
Looked that up, I'll try after my 2 current copy sessions end.
FWIW, the NVME formatting might also be relevant here. NTFS is likely slower than ext.
True, but I can't imaging that would reduce the 110 MB/s read of the disks down to 1/5. Also doesn't account for the wide range of speeds seen in the test results.
This one is surprising. It might be worth copying to /dev/null to test the read speed (in addition using dd to test read and write speeds of both devices).
This was in response to:
ssh > cp: 18 MB/s
cp -r -u -v "/data/Videos/2022/12/2022-12-20-063917.mkv" "/media/USB_HDD_7/Videos/2022/12/"
Just curious why this one was surprising to you...because it was also ssh and 2.5x the speed of rsync?
To me, the Biggest Surprise is how an over-the-network copy was several factors faster than a direct device copy?!?!? That makes zero sense...in fact opposite a reasonable hypothesis.
chadwixk
Dec 31, 2022Aspirant
Actually, I missed the 12% si utilization on the CPU summary in the TOP command pic. So CPU is pegged.
Another interesting thing I see on IOSTAT output is the %utilization of the read HDDs vs the write SSD and also the WAIT on the SSD?
The HDDs show pretty low utilization, and it's % util sort of corresponds with the % of actual to rated read speed...what would be holding this back? CPU/Memory is not designed in this such as to take full advantage of these slow HDDs?
The SSD shows very high utilization when the throughput is way less than capacity. I have no theories as to why this would be. Also note the WAITs for this. No clues on my end.
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