From mboxrd@z Thu Jan 1 00:00:00 1970 From: andy liebman Subject: Partitioning md devices versus partitioining underlying devices Date: Thu, 06 Apr 2006 11:25:14 -0400 Message-ID: <443532DA.7090809@aol.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: Sender: linux-raid-owner@vger.kernel.org To: linux-raid@vger.kernel.org List-Id: linux-raid.ids Hi, I have a fundamental question about WHERE it is best to do partititioning. Here's a concrete example. I have two 3ware RAID-5 arrays, each made up of 12 500 GB drives. When presented to Linux, these are /dev/sda and /dev/sdb -- each 5.5 TB in size. I want to stripe the two arrays together, so that 24 drives are all operating as one unit. However, I don't want an 11 TB filesystem. I want to keep my filesystems down below 6 TB. It seems I have two choices: 1) partition the 3ware devices to make /dev/sda1, /dev/sda2, /dev/sdb1 and /dev/sdb2. Then I can create TWO md RAID-0 devices -- /dev/sda1 + /dev/sdb1 = /dev/md1, /dev/sda2 + /dev/sdb2 = /dev/md2 OR 2) create /dev/md1 from the entire 3ware devices -- /dev/sda + /dev/sdb = /dev/md1 -- and then partition /dev/md1 into two devices. The question is, are these essentially equivalent alternatives? Is there any theoretical reason why one choice would be better than the other -- in terms of security, performance, memory usage, etc. A knowledgeable answer would be appreciated. Thanks in advance. Andy Liebman