Write image directly to disk

Mathieu Mitchell · Mathieu Mitchell · commit e53e297a5e92 · 2014-10-20T10:27:02.000-04:00
Write image directly to disk by telling qemu-img that the output
file is the disk. Still uses O_DIRECT directly within qemu-img.

This avoids the need to have a huge amount of system memory to be
able to deploy an image that contains a huge disk.

The only feature left behind by that commit is the 64K block size.

Change-Id: If60bcd82581b2ea76c4acbc3eaa3f317d2ee6590
diff --git a/ironic_python_agent/shell/write_image.sh b/ironic_python_agent/shell/write_image.sh
@@ -38,14 +38,8 @@ DEVICE="$2"
 log "Erasing existing mbr from ${DEVICE}"
 dd if=/dev/zero of=$DEVICE bs=512 count=10
 
-## Doing two steps allows us to use dd, which allows us to tweak things like
-## blocksize and allows use of direct io
-# Converts image to raw
-log "Converting $IMAGEFILE to RAW format"
-qemu-img convert -O raw $IMAGEFILE /tmp/image.raw
-
-# Write image onto device
-log "Imaging $DEVICE"
-dd if=/tmp/image.raw of=$DEVICE bs=64K oflag=direct
+log "Imaging $IMAGEFILE to $DEVICE"
+qemu-img convert -t directsync -O raw $IMAGEFILE $DEVICE
+sync
 
 log "${DEVICE} imaged successfully!"
