Solved What could cause this drop in copying speed?

I'm copying MR backup images from an NVMe to a USB-conected external SSD. I'd like to find out what causes this precipitous drop in copying speed at some point in the multiple-image-copying process, so that (maybe?) I could fix it. I've noticed this phenomenon during my last few backups from internal to external.

The Windows Defender and UAC is scanning the files been copied which will slow down speed.

Guessing... SLC cache may be full. Tell the model of your external (and internal) SSD. Then check at Tom's Hardware about the size of their SLC cache. may coincident.

Just noticed that the backup image being copied is the same in all three of my shots above, and wondered whether there might be something about that particular image that was gumming up the works, so I copied that image from the same internal to the same external again (this was after the time it took to get this OP up on the forum), with this result, so it ain't the image.

@FreeBooter That scanning behavior should be roughly constant throughout the transfer of files, shouldn't it?

@AndreTen Source is Samsung SSD 980 500GB, target is KINGSTON SA400S37240G : 240.0 GB on both my office computers (I mean, they're the same models, not the same disks; I have two externals, one for each machine, but the externals are the same model, size, and age, and so are the internals), but only this one (System 2 in my specs) shows this behavior.

Wisewiz said:

I'm copying MR backup images from an NVMe to a USB-conected external SSD. I'd like to find out what causes this precipitous drop in copying speed at some point in the multiple-image-copying process, so that (maybe?) I could fix it. I've noticed this phenomenon during my last few backups from internal to external.

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Noting to fix - speed changes when copying files are "normal".

I never copy backup images. The process can be time-consuming, and eventually cause corruptions.

Wisewiz said:

I'm copying MR backup images from an NVMe to a USB-conected external SSD. I'd like to find out what causes this precipitous drop in copying speed at some point in the multiple-image-copying process, so that (maybe?) I could fix it. I've noticed this phenomenon during my last few backups from internal to external.
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The explanation really is quite simple, and normal.

When copying data, it is initially copied to a RAM buffer which is faster than direct writing, but eventually depending on how much data is being written, the buffer gets filled, and data can only be added to buffer as fast as it is being written to the source drive.

You have no direct control over the size of the buffer but in simple terms, the more RAM you have, the bigger the buffer.

Note: whilst the buffer is being filled, data is being written to the target drive.

@cereberus 32GB RAM, @2400MHz, on this machine. I don't think I have any use for more RAM than that on this five-year-old PC.

Your use of "source" seems to differ from mine: I call the "source" the disk or file that's being copied; the "target" is the disk or folder it's being copied TO. Thanks for the explanation, though.

Have you monitored the temperatures of the devices (controller temperature in particular).

Well, yes, I monitored Crystal Disk Info while this was happening. Nothing warm there.

Wisewiz said:

Your use of "source" seems to differ from mine: I call the "source" the disk or file that's being copied; the "target" is the disk or folder it's being copied TO. Thanks for the explanation, though.

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yeah, my mistake - of course, I meant target.

Had you less than 32 gb, the "drop off" would occur much earlier.

Depending on number of files, and size tools like robocopy (multi-threading) or fastcopy can be a lot faster. It is rather pot luck though.

@cereberus Thanks again for your contribution to my understanding of this copying behavior. I'm glad I don't see it on my System 1.

@Anibor_11 I make backups of my backups all the time. It's extra insurance. And I periodically verify the backed-up backups with Macrium, to make sure they're still sound.

This is all interesting to me. You can see a HUGE difference in copy speeds if transferring between 2 NVMe "Pro" type drives (on the same motherboard connections) with the larger DRAM buffers the "pro" versions offer. However when copying between a fast NVMe drive and slower media, like Sata, USB, etc the speed differences become more noticeable.
I'd like to understand how the RAM buffer is sized by the OS and whether that is or can be user adjustable via some Registry entry. Perhaps not. But then there's the Buffer used on the target device as well. HDDs have much smaller buffers vs SSDs with DRAM buffering.(not the DRAM less ones)

On my daily driver PC I use a 2 TB NVMe drive for my "Desktop" drive. The "Desktop" that my OS uses.

@Wisewiz ,

Wisewiz said:

I make backups of my backups all the time. It's extra insurance. And I periodically verify the backed-up backups with Macrium, to make sure they're still sound.

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That makes two of us, at least. That's where I noticed the copy speed fluctuations during my weekly copy of my backup image to an external hard drive. Someone around here said: "You can never have too much backup."

Backup images on an internal backup drive or an always-connected external drive are potential victims of a ransomware attack, some variants of which target backup files.

Have a great day.

Regards,
Phil

Wisewiz said:

@FreeBooter That scanning behavior should be roughly constant throughout the transfer of files, shouldn't it?

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It depends on the size of the file, large files will take time to scan.