Copy to USB memory stick really slow?
Solution 1:
Why is copying to my USB drive so slow in Linux (and faster in Windows)?
Reason 1. File caching can make writes appear slower or faster
The problem I seem to see in the GUI is that the progress bar goes to 90% almost instantly, completes to 100% a little slower and then hangs there for 10 minutes.
One thing you need to understand is file caching. Linux (and Windows) will use otherwise "empty" RAM to cache read/write operations and make them faster on subsequent accesses. Caching copy operations to slow devices results in the behavior you see -- the "fast completion" is actually writing to the cache, and then it slows and stops because the actual flushing of the data in the cache (sync) to the slow device is taking very long. If you abort at that point, the data is corrupted (as you noted) since the sync never finished.
Such copying in Windows may seem faster (including the reported MB/sec speeds) because sometimes Windows will not wait for the sync, and declare the job completed as soon as the data is written to cache.
Reason 2. Writing lots of files, especially small ones, is slow
To copy 1.8GB
Because of the way flash memory and filesystems work, the fastest throughput (speed) is achieved when writing very large files. Writing lots of small files, or even mixed data containing a number of small files can slow the process down a lot. This affects hard drives too, but to a somewhat lesser extent.
Reason 3. Write speeds of a USB stick and an SSD cannot be compared
I have a super talent 32GB USB SSD in the neighboring port and it works at expected speeds.
A garden variety USB stick usually consists of flash memory chips that are written to serially (sequentially), and does not have any cache of its own.
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An SSD, on the other hand, contains a controller which writes to the flash memory chips parallel, increasing the throughput by a factor of 2 or more over the USB stick.
- If your 32GB SSD had 4x 8GB chips, it would still be 4x faster than the USB stick at any write operation.
- The SSD also contains RAM cache (like hard disks), so it can quickly store incoming data in the cache and tell the OS that it's done, while it still has to actually write that data to the flash memory.
So, with one large file, your 32GB GB with the 4x structure we assumed, would be 4x as fast; with many small files, it would be 10x or more faster because it could intelligently store them in its cache.
To sum up, these are the reasons why file copying to USB sticks may appear slower in Linux. Is it actually slower because of a hardware/driver issue or whatever....
Doing a proper comparison of write speeds between Linux and Windows
- First of all, forget about the SSD because of reason 3. It's like oranges and apples.
- To negate the effects of reason 1 (caching) and reason 2 (small files), you need to test with a single large file, larger than the amount of RAM on the test system.
- In Linux you can create it with
dd if=/dev/urandom of=largetest bs=1M count=7500, which gives you a 7500 MB test file. Assuming your system has less than 4GB or so of RAM, it's good enough. Copy that to a freshly formatted Sandisk 8GB stick, and time it. - Reboot in Windows, and copy
largetestfrom the USB stick to your hard disk. Reboot again (to remove it from the cache). Then format the USB stick (same vfat/FAT32!), and copylargetestfrom the hard disk to the stick. - How do the times compare?
Solution 2:
It's 2019 and I'm still having this same issue. So I figured I search the internet for a solution. I found the following page that suggests one: https://gist.github.com/2E0PGS/f63544f8abe69acc5caaa54f56efe52f
It says:
Execute the following commands in a console to see if it fixes the problem for you. You might need to sudo su first to have the required permission.
echo $((16*1024*1024)) > /proc/sys/vm/dirty_background_bytes
echo $((48*1024*1024)) > /proc/sys/vm/dirty_bytes
If it works you could make this change persistent across reboots by pasting the two lines at the end of your /etc/rc.local file.
For me it had the following effect:
Prior copying large files to an USB drive would start out really fast (like 60 MB/s) and become slower and slower (< 10 MB/s) until it looked like it would never finish.
Now it starts out slower, but gets faster and faster and finishes sooner than before. So it does seem to "solve" the problem or at least have a positive effect.
Solution 3:
Found the fix all i did was unmount, remove drive, and run sudo modprobe ehci_hcd in the Terminal. Insert drive and agian sudo modprobe ehci_hcd when I put the drive in and
wow 20/mbs thought i would share. Hope I dont have to do it every time... but it's not to hard...
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/177235 says they fixed the bug.