From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Brown Subject: Re: Creating an md with 3TB drives. Date: Thu, 29 Sep 2011 13:18:46 +0200 Message-ID: References: <4E82D53F.3050409@yazzy.org> <20110928182302.39cfd4b0@notabene.brown> <4E82DB7D.4050104@yazzy.org> <4E83388C.9010308@yazzy.org> <4E843917.9020606@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: <4E843917.9020606@yazzy.org> Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org List-Id: linux-raid.ids On 29/09/2011 11:23, Marcin M. Jessa wrote: > 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 > I did not know such drives existed - I thought all 2TB+ drives were 4K sector size. If these drives really have 512 byte sectors, then alignment will not be an issue.