On Thu, Mar 19, 2015 at 3:25 PM, Tom Horsley horsley1953@gmail.com wrote:
I see mdadm is one cryptic way to setup a software raid and I saw some note somewhere that says LVM also supports software raid1. Any reason one is better than the other (or does LVM not actually do raid and I misread something)?
It's mainly about which user space tool interface you prefer: mdadm or lvm. But about as important is the workflow. If you have a pile of drives, even mixed sizes, and your plan is to have multiple volumes with different kinds of redundancies (some raid1, raid5, raid6, maybe even raid0), and/or multiple volumes being created and destroyed with some frequency, you will prefer LVM raid because you get to define the raid level per LV.
mdadm has more user support on linux-raid@ so if you get stuck, chances are you're going to find a lot more help for mdadm raid than lvm raid.
Both mdadm and lvm use the kernel md driver on the backend. So it's the user space tools, and hence the on-disk metadata that differs. Performance should be about the same, any kernel md bugs would affect both mdadm and lvm raids.
My BIOS also has some sort of Intel raid helper hardware thing, but I can't imagine there would be a good reason to use it since all the data would become nearly inaccessible trash if I have to replace the motherboard :-).
Intel firmware RAID uses Intel IMSM metadata, which mdadm supports directly. The firmware reads this metadata and assembles the RAID right away such that it gets treated as a logical device in the pre-boot environment. Once that's exited during boot, the kernel md driver and mdadm take over. It is possible to assemble this type of RAID without an Intel motherboard.
If all you care about is mirroring two drives in the simplest way possible, this is certainly very simple, and it's also dual boot compatible.