Does dolphin `sync` disks after a move operation?

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1

After the move dialog is closed, can I be 100% sure that the data was completely transferred? i.e: no need to issue sync command?

2

We recently discussed this:

tl; dr: I believe that only unmounting the device will trigger a sync and you’ll get notified as soon as the device is ready to be unplugged.

3

The solution I’ve ended up using after doing searching on the issue was to set the vm.dirty_bytes and vm.dirty_background_bytes values so it causes the write cache to be flushed much quicker. I use the settings of 32 MiB for vm.dirty_bytes and 16MiB for vm.dirty_background_bytes.

You can change these values at runtime by using sysctl in a terminal (you may need to run sysctl with sudo depending on the user you’re using):

sysctl vm.dirty_bytes=33554432
sysctl vm.dirty_background_bytes=16777216

Setting the values low can affect IO bandwidth (mentioned in this LWN article), and if you’re using btrfs then it can’t be too low or it will reduce performance.

You can also create a config file in the /etc/sysctl.d/ directory, and name it something like 10-vm-settings.conf, then add the sysctl settings:

vm.dirty_bytes = 33554432
vm.dirty_background_bytes = 16777216

If you’re using btrfs then based on a Pop!_OS change, values of 256 MiB and 128 MiB for the respective parameters may be better.

vm.dirty_bytes = 268435456
vm.dirty_background_bytes = 134217728
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4

Linux kernel has a cache of data to be flushed to disks (dirty pages), and write operations done by apps are marked as done as soon as the output data has been written there.
In the general case this allows the kernel to optimize the write to disk operation, and on performant filesystems the delay is hard to notice.
This is not the case when the disk is slow (USB stick…).

We don’t have a way from the app to know if the data has been synced. We haven’t found a satisfying workaround. Calling sync is pretty bad for instance, as it blocks the thread.

Linux 6.5 cachestat syscall might help, will need to explore this after next glibc release.

https://sourceware.org/git/?p=glibc.git;a=commit;h=72511f539cc34681ec61c6a0dc2fe6d684760ffe

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5

This is reported in bug 281270 – When copying files to a removable disk, speed and progress reflect copying to the local cache not to the disk itself