From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from pigeon.gentoo.org ([208.92.234.80] helo=lists.gentoo.org) by finch.gentoo.org with esmtp (Exim 4.60) (envelope-from ) id 1NeuXG-0004zk-Bv for garchives@archives.gentoo.org; Tue, 09 Feb 2010 18:10:06 +0000 Received: from pigeon.gentoo.org (localhost [127.0.0.1]) by pigeon.gentoo.org (Postfix) with SMTP id 998A0E128F for ; Tue, 9 Feb 2010 18:10:05 +0000 (UTC) Received: from smtpout.karoo.kcom.com (smtpout.karoo.kcom.com [212.50.160.34]) by pigeon.gentoo.org (Postfix) with ESMTP id A2DEDE0F50 for ; Tue, 9 Feb 2010 17:17:51 +0000 (UTC) X-IronPort-AV: E=Sophos;i="4.49,437,1262563200"; d="scan'208";a="166112686" Received: from unknown (HELO compaq.stroller.uk.eu.org) ([213.152.39.90]) by smtpout.karoo.kcom.com with ESMTP; 09 Feb 2010 17:17:50 +0000 Received: from funf.stroller.uk.eu.org (funf.stroller.uk.eu.org [192.168.1.71]) by compaq.stroller.uk.eu.org (Postfix) with ESMTP id 19EFC13C90 for ; Tue, 9 Feb 2010 17:17:46 +0000 (GMT) Message-Id: <6A476A32-F164-4085-AA17-BAEE2584567C@stellar.eclipse.co.uk> From: Stroller To: gentoo-user@lists.gentoo.org In-Reply-To: <20100209154340.11d2ea18@zaphod.digimed.co.uk> Content-Type: text/plain; charset=US-ASCII; format=flowed; delsp=yes Content-Transfer-Encoding: 7bit Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-Id: Gentoo Linux mail X-BeenThere: gentoo-user@lists.gentoo.org Reply-to: gentoo-user@lists.gentoo.org Mime-Version: 1.0 (Apple Message framework v936) Subject: Re: [gentoo-user] 1-Terabyte drives - 4K sector sizes? -> bar performance so far Date: Tue, 9 Feb 2010 17:17:48 +0000 References: <5bdc1c8b1002070827i14f59047k39a695900ebe9889@mail.gmail.com> <20100209002757.0ec74d01@digimed.co.uk> <63F56C2B-97D3-4A98-9338-ED1D82FFAB1E@stellar.eclipse.co.uk> <201002091457.19162.joost@antarean.org> <702F5366-D38F-4B0C-BD52-1250CBFAC6CB@stellar.eclipse.co.uk> <20100209154340.11d2ea18@zaphod.digimed.co.uk> X-Mailer: Apple Mail (2.936) X-Archives-Salt: d5fc39bb-8eb2-41b3-bc77-d5e2b313d62a X-Archives-Hash: d7bc9706c1bdbde115ac42cdff9faeec On 9 Feb 2010, at 15:43, Neil Bothwick wrote: > On Tue, 9 Feb 2010 15:11:14 +0000, Stroller wrote: > >> You cannot remove one disk from the array and repartition it, because >> the partition is across the array, not the disk. The single disk, >> removed from a RAID 5 (specified by Paul Hartman) array does not >> contain any partitions, just one stripe of them. > > A 3 disk RAID 5 array can handle one disk failing. Although > information > is striped across all three disks, any two are enough to retrieve it. > > If this were not the case, it would be called AID 5. Of course you can REMOVE this disk. However, in hardware RAID you cannot do anything USEFUL to the single disk. In hardware RAID it is the controller card which manages the arrays and consolidates them for the o/s. You attach three drives to a hardware RAID controller, setup a RAID5 array and then the controller exports the array to the operating system as a block device (e.g. /dev/ sda). You then run fdisk on this virtual disk and create the partitions. You cannot connect just a partition to a hardware RAID controller. Thus in hardware RAID there are no partitions on each single disk, only (as I said before) stripes of the partitions. You cannot usefully repartition a single hard-drive from a hardware RAID set - anything you do to that single drive will be wiped out when you re-add it to the array and the current state of the virtual disk is propagated on to it. I hope this explanation makes sense. I was not aware that Linux software RAID behaved differently. See Joost's explanation of 9 February 2010 15:27:32 GMT. I asked if you were referring to LVM because I set that up several years ago, and it also allows you to add partitions as PVs. I can see how it would be useful to add just a partition to a RAID array, and it's great that you can do this in software RAID. So this: On 9 Feb 2010, at 00:27, Neil Bothwick wrote: > With the RAID, you could fail one disk, repartition, re-add it, > rinse and > repeat. But that doesn't take care of the time issue only applies in the specific case that Paul Hartman is using Linux software RAID, not the general case of RAID in general. Stroller.