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Linux is a family of open source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991 by Linus Torvalds. Linux is typically packaged in a Linux distribution (or distro for short).

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Linux file transfer speed bottlenecks? (midwest.social)

submitted 9 months ago* (last edited 9 months ago) by [email protected] to c/[email protected]

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I'm currently watching the progress of a 4tB rsync file transfer, and i'm curious why the speeds are less than the theoretical read/write maximum speeds of the drives involved with the transfer. I know there's a lot that can effect transfer speeds, so I guess i'm not asking why my transfer itself isn't going faster. I'm more just curious what the bottlenecks could be typically?

Assuming a file transfer between 2 physical drives, and:

Both drives are internal SATA III drives with ~~5.0GB/s~~ ~~5.0Gb/s read/write~~ 210Mb/s (this was the mistake: I was reading the sata III protocol speed as the disk speed)
files are being transferred using a simple rsync command
there are no other processes running

What would be the likely bottlenecks? Could the motherboard/processor likely limit the speed? The available memory? Or the file structure of the files themselves (whether they are fragmented on the volumes or not)?

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[–] [email protected] 2 points 9 months ago* (last edited 9 months ago) (1 children)

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[–] [email protected] 2 points 9 months ago (2 children)

Thanks, corrected my comment above.

I'm interested in ksmbd... I chose SMB simply because I was using it across lunix/windows/mac devices and I was using OMV for managing it, but that doesn't mean I couldn't switch to something better.

Honestly though, I don't need faster transfers typically, I just happen to be switching out a drive right now. SMB through OMV has been perfectly sufficient otherwise.

[–] [email protected] 5 points 9 months ago

ksmbd is still SMB, except it's implemented within the Linux kernel. As a result, file transfers speeds are improved greatly compared to pure-Samba which runs only in userspace.

The second thing is, you need to check which SMB protocol you're using, ideally you'd want to use at least SMB 3, anything older than that will be painfully slow.

Finally, I read in your other comment that you're using spinning disks and a USB dock. That adds significant overheads.

The Ironwolf drive benchmarks starting at 250MB/s and slows down to 100MB/s as it reaches the end of the drive. (spinning disks gradually become slower the more full it becomes.) Now add file fragmentation + filesystem overheads (buffers, cluster size allocation etc) and the speeds could go down considerably.

Then there's your SATA > USB dock - no dock would ever reach 5Gbps, that's just false advertising - it's only mentioning the theoretical protocol speed. In reality, you'd be seeing something like below 100MB/s write speeds for 128k sequential writes, but if your block size is smaller, expect far slower writes.

Combine all of the above and you can imagine just how much slower this whole thing can be.

For reference, see this benchmark as an example, to see what's "normal" for a simple file transfer to a blank drive with no fragmentation: https://www.anandtech.com/show/6014/startechcom-usb-30-to-sata-ide-hdd-docking-station-review/3