From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Marcin M. Jessa" Subject: Re: Creating an md with 3TB drives. Date: Thu, 29 Sep 2011 11:23:35 +0200 Message-ID: <4E843917.9020606@yazzy.org> References: <4E82D53F.3050409@yazzy.org> <20110928182302.39cfd4b0@notabene.brown> <4E82DB7D.4050104@yazzy.org> <4E83388C.9010308@yazzy.org> Reply-To: lists@yazzy.org Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: David Brown Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids On 9/29/11 11:09 AM, David Brown wrote: > On 28/09/2011 17:09, Marcin M. Jessa wrote: >> On 9/28/11 10:43 AM, David Brown wrote: >>> On 28/09/2011 10:31, Marcin M. Jessa wrote: >>>> On 9/28/11 10:23 AM, NeilBrown wrote: >>>> [...] >>>> >>>>>> >>>>>> Then I used fdisk to change the partition type to Linux raid auto >>>>> >>>>> You can do that if you like but it will have no effect. The "raid >>>>> auto" >>>>> partition type only means anything on MBR partitions. You don't need >>>>> to, so >>>>> don't bother. >>>> >>>> Thanks Neil. >>>> Not using fdisk worked like a charm. >>>> >>> >>> Using fdisk probably resulted in the disks going over to MBR rather than >>> GPT, and thus you have a 2TB limit. >>> >>> By the way, you should probably try the parted again and fix the >>> alignment issue (rather than just "ignoring" it) - it will make a /big/ >>> difference. >> >> In terms of speed? >> This RAID array is temporarily just so I can back up/restore my broken >> 5x2TB RAID6 but it would be interesting to know what to do. >> I was running >> # parted -a optimal /dev/sdd >> which was suppose to fix that warning but it didn't. >> > > Yes, I was thinking in terms of speed. I haven't gone beyond 2 TB disks > with MBR myself, so I can't comment on whether your partitions really > are misaligned, or if it is just an incorrect warning. But if these > disks are like most 2 TB disks with 4K sectors but which lie and claim > to have 512 byte sectors (for compatibility with ancient and inferior > OS'es), then partition misalignment will be major performance hit. It's > worth double-checking that you've got it right here, before you go to > far with the array. These are 3TB Hitachi drives and Hitachi kept 512 byte sectors: http://www.hitachigst.com/internal-drives/desktop/deskstar/deskstar-7k3000 -- Marcin M. Jessa