New Setup Pool Configuration (Hard Disks)

[Yell]

Greetings, I want to move from my linux selfbuild mdadm setup (Fedora 15-netinstall) to ZFS.

This machine will run with the following Hardware with all drives in a Raidz2:

• Mainboard: Intel DH55TC (6x Sata 3G onboard)
• CPU: Intel Core i3 530 2.93GHz
• RAM: 2x 4GB (KIT)+ 1x 2GB
• Disks: 4x WD20earS + 2 WD20earX (one RMA, one new)
• Case: Aerocool Vs-9 Advance Midi-Tower ATX, will use it like an Rackmount 2HE on my desk ;)
• HotSwap: 2x Xigmatek 3in3 Hot-Swap HDD Cage
• PSU: be quiet! Pure Power 300 Watt / BQT L7 (which is in use for over 2 years with 5x 2TB disks)

I've gathered lots of information, but there is one thing that doest fit well:

Storage Pools
Set up one storage pool using whole disks per system, if possible.
..
For production systems, use whole disks rather than slices for storage pools for the following reasons

Source: http://www.solarisinternals.com/wik...ices_Guide#ZFS_Storage_Pools_Recommendations]

Storage Disks and Controllers
..
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.

Source: http://doc.freenas.org/index.php/Hardware_Recommendations

So why does the WebGUI of FreeNAS creates a 2GB Partition on each drive, if a "whole disk" is recommended?
Do i need this (Raid 0 ?) swap in my hardware setup or is it stability concern for this low-RAM-overpriced-buy-me-now-NAS boxes?

 

[ben]

An almost full disk is almost impossible to write to because of all the seek time needed to find some empty space. ZFS will underprovision a disk by 2GB in order to reserve space for new writes. This is WHY we suggest giving a full disk - it lets the filesystem do tricks like that.