From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mario 'BitKoenig' Holbe Subject: Why is sb->size set to 0 with raid0? Date: Wed, 21 Jul 2010 18:16:46 +0200 Message-ID: Return-path: Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org List-Id: linux-raid.ids Hello, while examining a raid0 v1.2 superblock I found "Used Dev Size" seems not to be set there, mdadm -E on a component device shows: Magic : a92b4efc Version : 1.2 Feature Map : 0x0 ... Avail Dev Size : 2930274824 (1397.26 GiB 1500.30 GB) Used Dev Size : 0 Data Offset : 16 sectors Super Offset : 8 sectors State : clean Is this intentional? This is just to let you know and for my curiosity. I don't know whether this has negative side-effects or not. I found none until now. Don't get me wrong, I like the (IMHO positive) side-effect of this: it makes totally sense to me, not to reserve bitmap-space for raid0 - I even downgraded to mdadm 3.1.1 for raid creation to get rid of the 1M alignment, and I was short thinking about patching super1.c for this array to get rid of the bitmap-space reservation as well. Thus, I was just positively surprised to see that in fact there *is* no bitmap-space reserved for raid0, wondered how and where this was managed, and tracked it down to sb->size being set to 0. regards Mario -- You know, people think mathematics is complicated. Mathematics is the simple bit. Its the stuff we can understand. Its cats that are complicated. I mean, what is it in those little molecules and stuff that make one cat behave differently than another, or that make a cat? And how do you define a cat? I have no idea. -- John Conway