1.4.4 Storage Disks and Controllers
The Disk section of the FreeBSD Hardware List lists the supported disk controllers. In addition, support for 3ware 6gbps RAID controllers has been added along with the CLI utility tw_cli for managing 3ware RAID controllers.
FreeNAS® supports hot pluggable drives. Make sure that AHCI is enabled in the BIOS. Make sure that AHCI is enabled in the BIOS. Note that hot plugging is not the same as hot swapping.
If you need reliable disk alerting, immediate reporting of a failed drive, and or swapping, use a fully manageable hardware RAID controller such as a LSI MegaRAID controller or a 3Ware twa-compatible controller. Until FreeBSD commits zfsd, its implementation of ZFS will not notice that a drive is gone until you reboot or put the volume on high load.
If you have some money to spend and wish to optimize your disk subsystem, consider your read/write needs, your budget, and your RAID requirements.
For example, moving the the ZIL (ZFS Intent Log) to a dedicated SSD only helps performance if you have synchronous writes, like a database server. SSD cache devices only help if your working set is larger than system RAM, but small enough that a significant percentage of it will fit on the SSD.
If you have 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.
7200 RPM SATA disks are designed for single-user sequential I/O and are not a good choice for multi-user writes.
If you have the budget and high performance is a key requirement, consider a Fusion-I/O card which is optimized for massive random access. These cards are expensive and are suited for high end systems that demand performance. A Fusion-I/O can be formatted with a filesystem and used as direct storage; when used this way, it does not have the write issues typically associated with a flash device. A Fusion-I/O can also be used as a cache device when your ZFS dataset size is bigger than your RAM. Due to the increased throughput, systems running these cards typically use multiple 10 GigE network interfaces.
If you will be using 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, you can not format less than 3 GB of space with ZFS. However, on a drive that is below the minimum recommended size you lose a fair amount of storage space to swap: for example, on a 4 GB drive, 2 GB will be reserved for swap.
If you are new to ZFS and are purchasing hardware, read through ZFS Storage Pools Recommendations first.
ZFS uses dynamic block sizing, meaning that it is capable of striping different sized disks. However, if you care about performance, use disks of the same size. Further, when creating a RAIDZ, only the size of the smallest disk will be used on each disk.
