inconsistency in drive allocation

Defining a client, via virt-manager, drive allocation seems inconsistent.
On some (DSL, pfSense), the primary HDD is allocated as hdb, and on others (ibex) as hda.

On host:

sudo virsh dumpxml dsl

Connecting to uri: qemu:///system
<domain type='kvm' id='5'>
  <name>dsl</name>
  <uuid>a31756b8-a748-c783-3313-8c95ffff58ea</uuid>
  <memory>524288</memory>
  <currentMemory>524288</currentMemory>
  <vcpu>1</vcpu>
  <os>
    <type>hvm</type>
    <boot dev='cdrom'/>
  </os>
  <features>
    <acpi/>
  </features>
  <clock offset='utc'/>
  <on_poweroff>destroy</on_poweroff>
  <on_reboot>restart</on_reboot>
  <on_crash>destroy</on_crash>
  <devices>
    <emulator>/usr/bin/kvm</emulator>
    <disk type='file' device='disk'>
      <source file='/home/jaco/vm/dsl.img'/>
      <target dev='hda' bus='ide'/>
    </disk>
    <disk type='file' device='cdrom'>
      <source file='/home/jaco/Downloads/_lin_/_distros_/desktop/dsl-4.4.10.iso'/>
      <target dev='hdc' bus='ide'/>
      <readonly/>
    </disk>
    <interface type='bridge'>
      <mac address='00:16:3e:75:f0:bb'/>
      <source bridge='br0'/>
      <target dev='vnet3'/>
    </interface>
    <input type='mouse' bus='ps2'/>
    <graphics type='vnc' port='5903' listen='127.0.0.1'/>
  </devices>
</domain>

ps aux | grep dsl

root 14528 1.6 2.6 646260 108580 ? S 12:08 1:30 /usr/bin/kvm -M pc -m 512 -smp 1 -monitor pty -drive file=/home/jaco/Downloads/_lin_/_distros_/desktop/dsl-4.4.10.iso,if=ide,media=cdrom,boot=on -drive file=/home/jaco/vm/dsl.img,if=ide -net nic,macaddr=00:16:3e:75:f0:bb,vlan=0 -net tap,fd=18,script=,vlan=0 -usb -vnc 127.0.0.1:3

on client:

sudo fdisk -l

Disk /dev/hdb: 1048 MB, 1048576000 bytes
255 heads, 63 sectors/track, 127 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

   Device Boot Start End Blocks Id System
/dev/hdb1 * 1 127 1020096 83 Linux