[arch-general] RAID10 + dmcrypt/LUKS + ext4: expanding?

[Guus Snijders]

Op 25 okt. 2017 03:53 schreef "L. Rose" <lists at lrose.de>:

Hi everyone,

I want to setup a couple of drives using RAID10 with mdadm. On top of
/dev/md0, I want to setup one large dmcrypt/LUKS encrypted ext4 volume.
As Arch wiki reads, this seems to be possible. But what about expanding
that volume later on? RAID#Format_the_RAID_Filesystem recommends
calculating the stripe_width value for ext4 based on the number of data
disks[0]. When adding a new disk, the number of data disks would
increase by one, and expanding both the dmcrypt/LUKS and the ext4 layer
should be possible - but what about the stripe width_value? Does it need
to be updated? Should it be updated? Is it possible to update the
stripe_width value afterwards?

[...]

[0]: https://wiki.archlinux.org/index.php/RAID#Example_3._RAID10.2Cfar2


Regarding the (md)stripe_width: with the F2 layout, you can just add a 3rd
drive without worry. Take a *good* look at the Linux MD Raid documentation
(not just the ArchWiki) and you'll see that F2 always uses *blocks* in
pairs, not disks.

That is a major difference between software RAID and hardware Raid.


Mvg, Guus Snijders