Is there any way to change the way the Linux kernel handles external storage and the external storage cache? Every time I copy something to it, the copy process seen from userspace seems really fast. I have seen this behaviour many times while copying files, but I just noticed that it also happens when I am copying data with
dd directly to the drive. So nothing is mounted here!
Copying a .iso image:
$ sudo dd if=/mnt/mountpoint/Fedora-Live-Workstation-x86_64-23-10.iso of=/dev/sdc 2869248+0 Datensätze ein 2869248+0 Datensätze aus 1469054976 Bytes (1,5 GB) kopiert, 13,8922 s, 106 MB/s $ sync
The first command takes 13s, but the second sync stage takes 90 secs or so.
Why is so much data (over 1,3 GB) held in cache? Is there any possibility of avoiding this behaviour?
If this is relevant for you. I am using a Ubuntu 15.10 4.2.0-34-generic standard kernel and it is a USB 2.0 usb-drive.