Yelläks /ˈyæl•eks/

I experienced slow USB mass storage devices such as USB pen drives, attached to a USB2.0 port. The writing speed usually did not cross 600KB/sec. To solve the problem I am mounting the pen drive with the async option set.

The manual of mount in NetBSD says about async:

All I/O to the file system should be done asynchronously. In the event of a crash, it is impossible for the system to verify the integrity of data on a file system mounted with this option. You should only use this option if you have an application-specific data recovery mechanism, or are willing to recreate the file system from scratch.

Since I am using pen drives to move data only e.g. for a presentation, it is no big issue to reformat the pen drive in case of a crash. With async set the writing speed increases to around 8MB/sec. To make the change persistent, add async in your fstab:

/dev/sdb1 /media/usb0 auto noauto,noatime,nodiratime,user,rw,exec,suid,async,uid=1000,gid=1000,umask=0072 0 0

Or, if you use usbmount to mount the pen drives automatically add async to the MOUNTOPTIONS in /etc/usbmount/usbmount.conf

It is always a good idea to sync or to umount the drives before you unplug them.