On Wed, Jul 3, 2013 at 11:08 AM, David Lehman <dlehman@xxxxxxxxxx> wrote:
I'm not a sysadmin either, nor am I a RAID expert, but my understandingis that raid10 on <4 disks is actually RAID1E. Blivet doesn't support
RAID1E, regardless of what mdadm calls it.
RAID-1E is one of those things that is kinda like EIDE.
EIDE was actually a[n] (unenforced? or little enforced?) trademark of Western Digital used to describe certain set of register setup for 16/32-bit bus/data Programmed I/O (PIO) modes. It then ended up being used generically by most people, even though the ATA specifications created a superset of EIDE which wasn't always 100% EIDE compatible either (let alone added DMA). Even EIDE was eventually used by the ATA Consortium itself to describe it.
So as I understand it, IBM-LSI RAID-1E is more of the same. RAID-1E on a IBM or LSI card might be slightly different than the various modes in the SNIA's Commmon RAID Disk Data Format (DDF) Specification. The latter really doesn't define "the standard" but takes a "technical position" on layout (e.g., adjacent, off-set, etc...). [1] As with most MD (or DM for that matter), auto-detection with [Fake] RAID, one must take care to get exactly, or not at all.
I like to call it "striped-mirrors," and explicitly differentiate from "striping + mirroring," both of which is far more exacting of a statement.
> Blivet doesn't support RAID1E, regardless of what mdadm calls it.
Well, if there is one thing I've learned to understand about mdadm, it doesn't try to call any RAID something that is not already in use. When in doubt, it defines formats without a name, and merely assigns a label for an option. This is not unlike most open source technology (e.g., Samba comes to mind), it forces implementers and integrators to understand _more_ technical details that are far more _exacting_ than just a single name or label.
Wikipedia has a good, quick intro of 'Non-Standard' "striped-mirrors" between both mdadm [2] and RAID-1E [3]. Although I guess you could say that any RAID-1E that follows DDF definition for RAID-1E is not exactly 'Non-Standard.' The question is, what modes do and don't fit IBM-LSI implementations?
-- bjs
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