The "Linux Raid Autodetect" (fd) type: what is it?

abolishtheun · 03-21-2009, 01:46 AM

The software RAID howto's keep saying that partitions to be used in raid arrays should be of the type "Linux Raid Autodetect" ('fd' in fdisk). However, using the usual type Linux (83) doesn't seem to inhibit mdadm from creating a disk or assembling it after boot. So my questions are:

What exactly are the differences between the types 83 and fd?

What is autodetected and when?

Any other wisdom appreciated.

vindoan · 03-21-2009, 02:26 AM

From "The Software-RAID HOWTO" (http://www.tldp.org/HOWTO/Software-R...O-7.html#ss7.2),

Autodetection allows the RAID devices to be automatically recognized by the kernel at boot-time, right after the ordinary partition detection is done.

"This requires several things:

1. You need autodetection support in the kernel. Check this
2. You must have created the RAID devices using persistent-superblock
3. The partition-types of the devices used in the RAID must be set to 0xFD (use fdisk and set the type to "fd")"

Why would you want this? See http://www.tldp.org/HOWTO/Software-R...O-5.html#ss5.9 .

abolishtheun · 03-21-2009, 02:50 AM

thanks, my google-fu is off tonight, should've seen that.