The Disk section of the FreeBSD Hardware List lists the supported disk controllers. In addition, support for 3ware 6 Gbps RAID controllers has been added along with the CLI utility tw_cli for managing 3ware RAID controllers.
FreeNAS® supports hot pluggable drives. Using this feature requires enabling AHCI in the BIOS.
Reliable disk alerting and immediate reporting of a failed drive can be obtained by using an HBA such as an Broadcom MegaRAID controller or a 3Ware twa-compatible controller.
Upgrading the firmware of Broadcom SAS HBAs to the latest version is recommended.
Some Highpoint RAID controllers do not support pass-through of S.M.A.R.T. data or other disk information, potentially including disk serial numbers. It is best to use a different disk controller with FreeNAS®.
The system is configured to prefer the mrsas(4) driver for controller cards like the Dell PERC H330 and H730 which are supported by several drivers. Although not recommended, the mfi(4) driver can be used instead by removing the loader Tunable: hw.mfi.mrsas_enable or setting the Value to 0.
Suggestions for testing disks before adding them to a RAID array can be found in this forum post. Additionally, badblocks is installed with FreeNAS® for testing disks.
If the budget allows optimization of the disk subsystem, consider the read/write needs and RAID requirements:
- For steady, non-contiguous writes, use disks with low seek times. Examples are 10K or 15K SAS drives which cost about $1/GB. An example configuration would be six 600 GB 15K SAS drives in a RAID 10 which would yield 1.8 TB of usable space, or eight 600 GB 15K SAS drives in a RAID 10 which would yield 2.4 TB of usable space.
For ZFS, Disk Space Requirements for ZFS Storage Pools recommends a minimum of 16 GB of disk space. Due to the way that ZFS creates swap, it is not possible to format less than 3 GB of space with ZFS. However, on a drive that is below the minimum recommended size, a fair amount of storage space is lost to swap: for example, on a 4 GB drive, 2 GB will be reserved for swap.
Users new to ZFS who are purchasing hardware should read through ZFS Storage Pools Recommendations first.
ZFS vdevs, groups of disks that act like a single device, can be created using disks of different sizes. However, the capacity available on each disk is limited to the same capacity as the smallest disk in the group. For example, a vdev with one 2 TB and two 4 TB disks will only be able to use 2 TB of space on each disk. In general, use disks that are the same size for the best space usage and performance.
The ZFS Drive Size and Cost Comparison spreadsheet is available to compare usable space provided by different quantities and sizes of disks.