[jensv]

md is multiple devices. It's a RAID implementation in Linux kernel available since kernel release 2.0. It allows you to create RAID level 0, 10, 4, 5 and 6. It has various optimizations like utilizing SSE and MMX instructions. It's a standard software RAID in Linux.

[babuskov]

> It allows you to create RAID level 0, 10, 4, 5 and 6.

I'm pretty sure it supports RAID level 1 as well:

https://raid.wiki.kernel.org/index.php/RAID_setup#RAID-1

Or am I misunderstanding something?

[dspillett]

It does. Also the less standard RAID10-over-three-devices (similar to the scheme called RAID1E by some hardware RAID controllers, though with more layout options than they usually supply).

[rincebrain]

At first I thought you were describing a 3-way mirror, then I looked into it, and that's a cleverly kinky idea.

[nailer]

I thought it was 'meta devices'? Hrm the docs don't actually say: https://raid.wiki.kernel.org/index.php/A_guide_to_mdadm

[tyingq]

Here's a 2002 reference to mdadm being referred to as "multiple devices admin".

https://web.archive.org/web/20180211041128/www.linuxdevcente...

[throwaway2048]

it does many things besides RAID, its more or less a generic "do things with abstracted block layers" tool these days.

[thoxahr]

The similarly named "dm" (device mapper) is a generic abstract block layer tool. md is still specifically a software raid implementation.