[ubuntu] Using ext4 loopback image

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http://ubuntuforums.org – I've created a 8GB disk image (ext4) from a partition of USB flash drive via 'dd'. I mount it to a directory: mount -o loop disk.img mount_dir/ I can access the files inside it. The problem is that when I copy files to the mount_dir, the system seems to have large IO Wait and the system is nearly hang. I also tried to copy only few small files. Though the 'cp' command is returned quickly, it takes long time to finish a following 'sync' command. This gives me an impression that, when the system flush the data to a disk image, it will re-write the whole image file again. Thus, in my case, (Hardware)