Arrays are built on top of block devices; typically disks.
This leads to 2 frequent questions:
- Should I use entire device or a partition?
- What partition type?
There is no right answer - you can choose.
Entire Devices or Partitions
Your editor prefers to use partitions that are slightly smaller than a device. This allows:
- the device has a partition table - no 'partition table not found'
- replacement disks even of the same model are often slightly smaller and making the partition 100Mb smaller than the device allows some tolerance.
- no performance impact
Neil, the md/mdadm author, uses whole disks.
What Partition Type
If you are using partitions then there are only 2 sensible choices for your partition type:
- 0xDA for non-fs data
- 0xFD for old autodetect arrays
(From the mdadm 2.6.8 man-page) When creating partition-based arrays using mdadm and version-1.x superblocks, the partition type should be set to 0xDA (non fs-data). This type selection allows for greater precision since using any other type [RAID auto-detect (0xFD) or a GNU/Linux partition (0x83)], might create problems in the event of array recovery through a live cdrom.