From mboxrd@z Thu Jan 1 00:00:00 1970 From: Oliver Schinagl Subject: Re: Odd --examine output Date: Mon, 15 Apr 2013 18:06:36 +0200 Message-ID: <516C258C.7070406@schinagl.nl> References: <10112252.14.1366051374769.JavaMail.root@zimbra> <20844.24431.814932.275104@quad.stoffel.home> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20844.24431.814932.275104@quad.stoffel.home> Sender: linux-raid-owner@vger.kernel.org To: John Stoffel Cc: Roy Sigurd Karlsbakk , Mike Vanhorn , Phil Turmel , Linux RAID List-Id: linux-raid.ids On 15-04-13 22:13, John Stoffel wrote: >>>>>> "Roy" == Roy Sigurd Karlsbakk writes: >>>> NOT a guess. Back up what you can, while you can, and start over. Use >>>> "fdisk -u" so you can ensure partitions start on multiples of eight >>>> (8) >>>> sectors. (Modern fdisk uses 1MB alignment by default. Highly >>>> recommended.) >>>> >>>> >>> So, if I start the partition at sector 64 (rather than 63), that's >>> better, >>> right (since 64 is a multiple of 8)? Or is there more math to do and >>> I'm still not getting it? > Roy> I still don't understand why people use partitions for RAID when > Roy> the whole drive is used anyway. Partitions were invented to > Roy> partition things up and are of no use if you want to spend the > Roy> whole drive's space for RAID use (or otherwise). > > Because if I take a 2tb disk a I put a partition on there which is a > bit smaller than the full disk, if I then add a new 2tb (or any other > size) disk which says it's 2tb, but it's really a bit smaller, then > I'm not screwed. I've had it happen. Or if you use them for your OS, and have several raids for /, /usr, /var etc. Or you buy 2 or 3 batches of disks, all varying sizes (1TB != 1TB) and having partitions allows you to at least align them all to the same size. And its even possible to buy a replacement disk, that's actually larger but cheaper as prices came down. A strange use case could be that 1 disk split into 2 partitions could be a hot-spare for 2 arrays. When using 1MiB offsets for partitions, I don't think there's any performance loss at all (due to alignment) nor will it slow down anything because md is on a partition rather then a disk. Wasting 1 MiB per disk is really not significant. And when using raid1/10 it allows you in theory to wipe the superblock and make the partition point tot he real data; though there's very little use for that imo. I personally, don't see why you want to use the entire disk, is there any advantage? > > John > -- > To unsubscribe from this list: send the line "unsubscribe linux-raid" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html