===== VirtualBox on FreeBSD Tuning Guide =====

==== Timer frequency ====
Kernel's timer frequency ("HZ") in %%FreeBSD%% 6.x and above is set to a relatively large value - 1000 Hz. While beneficial on real hardware, High HZ setting has a negative impact on simulated machine's performance because the VM host software spends too much time handling timer interrupts, which causes context switches, cache flushes and other performance-hindering operations. %%FreeBSD%% 9.0 autodetects if it is running as [[/VirtualBox|VirtualBox]] guest and sets ''%%kern.hz%%'' to 100 automatically.

/boot/loader.conf in the Guest:

<code>
# Decrease timer frequency for better performance
kern.hz=100
</code>

==== Bridged Network ====

If you use bridged networking and transfer big chunks over the network or have heavy network load netgraph probably runs out of memory.

/boot/loader.conf on the Host:

<code>
# Increase netgraph memory size for heavy VirtualBox network load
net.graph.maxdata=65536
</code>

==== Harddisk ====

[[/VirtualBox|VirtualBox]] can emulate ATA and SATA controllers but defaults to ATA for %%FreeBSD%% guests. %%FreeBSD%% also supports SATA and AHCI and performance is a lot better if you have AHCI enabled on the host and the guest. Since %%FreeBSD%% 9.0 the new CAM infrastructure is enabled per default so you already see your devices as ''%%/dev/ada0%%''. For %%FreeBSD%% 8.x you need to explicitly enable it but beware - your device names will change from ''%%/dev/ad0%%'' to ''%%/dev/ada0%%'' so you probably have to modify your ''%%/etc/fstab%%'' too.

/boot/loader.conf for %%FreeBSD%% 8.x on the Host and Guest:

<code>
ahci_load="YES"
</code>

[[/VirtualBox|VirtualBox]]:
1. Go to Virtual Machine settings, switch to "Storage" tab;
{{virtualbox/tuning/addsata_init.png?linkonly|addsata_init.png}}

2. On the bottom of the devices list, click "Add Controller", then "Add new SATA controller"
{{virtualbox/tuning/addsata_step1.png?linkonly|addsata_step1.png}}

3. Click "Add new disk", "Add new Hard disk"
{{virtualbox/tuning/addsata_step2.png?linkonly|addsata_step2.png}}

4. Select existing drive or create a new one.

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[[/CategoryVirtualization]]