Question USB copying - Data Transfer

[sargan]

I have been copying a lot of data to a selection of USB drives (FAT 32)
When I start the copy .... its runs at a reasonable constant 34-38MB/s
Everytime though once 4 or 5 mins into copying across data, the rate slows down to 7-8MB/s and stays that way until copy is complete .... this is not reaching capacity as stioll more than 25% left empty.

Why is this ?

 

[USAFRet]

I have been copying a lot of data to a selection of USB drives (FAT 32)
When I start the copy .... its runs at a reasonable constant 34-38MB/s
Everytime though once 4 or 5 mins into copying across data, the rate slows down to 7-8MB/s and stays that way until copy is complete .... this is not reaching capacity as stioll more than 25% left empty.

Why is this ?

The cache space on the flash drive fills up.

Once there, speed reduces.

Also, composition of the data. A lot of tiny files will transfer a lot slower than a single drive of the same cumulative size.


It is what it is.

 

[cgilley]

yup, caching issue all the way. A few years ago, I purchased a couple of 128GB usb thumb drives that said something like "super-dooper-really-fast." I forget the speed quoted but the devices were USB 3.0 so I expected 3.0 performance. Moving files, I was really disappointed with the performance, did some research, found some USB drive test software, and learned a lot.

Basically, most of the specs on USB devices simply just lie. Once that cache fills up, it's a turd.

 

[cgilley]

Here is an interesting tidbit. I'm in the middle of cleaning up my development laptop. I've "retired" - that's a d**** joke, but I'll stay on topic. I

I have been copying a lot of data to a selection of USB drives (FAT 32)
When I start the copy .... its runs at a reasonable constant 34-38MB/s
Everytime though once 4 or 5 mins into copying across data, the rate slows down to 7-8MB/s and stays that way until copy is complete .... this is not reaching capacity as stioll more than 25% left empty.

Why is this ?

have a 1TB WD spinner that is having sustained I/O at 110MB/s. I have never seen a USB SSD keep up with that. I'll have to test again and plan too. I'll update my post this evening.

Okay, after testing, here is what I've come up with. I'm moving LARGE files (100GB+) over a USB3 connection. The spinner, read and write pushes 100MB/sec. I have a sandisk SSD - 34 MB/sec write 42 MB/sec read.

Sandisk is mostly empty. Performance really depends on the microcontroller inside the device, and most of them suck.

Wikipedia: USB 3.0 has transmission speeds of up to 5 Gbit/s or 5000 Mbit/s, about ten times faster than USB 2.0 (0.48 Gbit/s) even without considering that USB 3.0 is full duplex whereas USB 2.0 is half duplex.

In all my years, I have never seen performance at that level. Not for read/write to storage devices. Maybe for video. I've seen this cache issue with industrial grade devices across the board. Commercial is worse.

IT's not you.