All FreeBSD 9.0 and later installations come with GPT. You can use gpart(8) instead of the classic fdisk(8) and disklabel(8).
AHCI - Advanced Host Controller Interface is a standard for disk drives and controllers. Enabling AHCI in the BIOS can give a 5-15% performance increase. Not all controllers offer AHCI.
For Solid State Computer Systems most SSD models support a feature called TRIM. TRIM is just a status update that triggers when the filesystem deletes a block, it also notifies the device that the block is no longer in use. The SSD firmware can then do some wear leveling functions. Without TRIM, it would not be able to tell whether that block was still in use. TRIM does not require AHCI.
Some Commands
To remove existing partitions from a drive
gpart delete
gpart show
gpart recover vtbd0
gpart add -t freebsd-ufs -b BEGIN -s SIZE GEOM
gpart add -t freebsd-ufs -b 20971682 -s 18874240 vtbd0
newfs -U /dev/vtbd0p4
mkdir /transip
mount /dev/vtbd0p4 /transip
mount /dev/vtbd0p4 /transip
Partition a SSD for FreeBSD
Applies to Solid State Computer Systems with FreeBSD 10.X and newer.
Do not enable TRIM unless the SSD supports it. Better yet, avoid SSDs that do not support TRIM.
Create the partition scheme. In the GPT partition scheme make a boot partition of the size 512K. Here we will use the new 4K-alignment which is what is advised for SSD drives. More information is on Hard Drive Logical Block Format Migration to 4K- Alignment.
gpart create -s gpt ada0 gpart add -t freebsd-boot -s 512k -a4k -l ssdboot ada0 gpart bootcode -b /boot/pmbr -p /boot/gptboot -i1 ada0
Now create a root partition. 2GiG is recommended. Unique naming is recommended. The 1M location is 4K aligned and 1M aligned.
gpart add -t freebsd-ufs -l ssdrootfs -b 1m -s 2g ada0
2G partition for /var and the rest of the SSD for /usr.
gpart add -t freebsd-ufs -l ssdrootfs -b 1m -s 2g ada0 gpart add -t freebsd-ufs -l ssdvarfs -a 1m -s 2g ada0 gpart add -t freebsd-ufs -l ssdusrfs -a 1m ada0
Fresh installation of FreeBSD on a SSD may use the newfs(8) the filesystems without TRIM. Boot into single user mode and use tunefs(8) -t enable to re-enable it on each filesystem. FreeBSD’s UFS filesystem supports TRIM. That will be enabled with -t while formatting the filesystems.
Format these file systems with TRIM enabled
newfs -U -t /dev/gpt/ssdrootfs newfs -U -t /dev/gpt/ssdvarfs newfs -U -t /dev/gpt/ssdusrfs
The FreeBSD installer might format the file system without enabling TRIM. You can go in after the fact and enable TRIM by doing the following when booted into single user mode:
tunefs -t enable /dev/gpt/ssdrootfs tunefs -t enable /dev/gpt/ssdvarfs tunefs -t enable /dev/gpt/ssdusrfs
Now to deal with SSD specific things. /etc/fstab must be changed to refer to the SSD. At the same time, the missing /tmp will be added.