Monitoring Long Running IO Commands with pv

June 18, 2012

Setting up a virtual machine environment means moving around a lot of big files. I prefer to use raw LVM disk images for virtual machines, as they have fewer IO bottlenecks and allow live backups through the LVM Snapshot functionality. This also means I spend a lot of time moving around logical volume data on the command line with dd. These transfers can take anywhere from a couple minutes to an hour depending on the size.

I use the pv Pipe Viewer utility to track progress. As the name implies, it works by tracking data moving through piped commands. Using it is just a matter of placing it between two commands via pipes. So:

dd if=/dev/mapper/vg-lv1 of=/dev/mapper/vg-lv2

becomes:

dd if=/dev/mapper/vg-lv1 | pv | dd of=/dev/mapper/vg-lv2

When executed the data throughput is displayed in realtime.

Depending on the commands piping data to pv it not only displays current progress, but also time remaining. There are packages available for apt and yum.