From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Joachim Otahal (privat)" Subject: Re: RAID5 with two drive sizes question Date: Tue, 05 Jun 2012 21:41:39 +0200 Message-ID: <4FCE60F3.4040606@gmx.net> References: <4FCE4199.7030705@gmx.net> <20120605233953.2086cc4c@natsu> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20120605233953.2086cc4c@natsu> Sender: linux-raid-owner@vger.kernel.org To: Roman Mamedov Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids Roman Mamedov schrieb: > On Tue, 05 Jun 2012 19:27:53 +0200 > "Joachim Otahal (privat)" wrote: > >> Hi, >> Debian 6.0.4 / superblock 1.2 >> sdc1 = 1.5 TB >> sdd1 = 1.5 TB (cannot be used during --create, contains still data) >> sde1 = 1 TB >> sdf1 = 1 TB >> sdg1 = 1 TB >> >> Target: RADI5 with 4.5 TB capacity. >> >> The normal case would be: >> mdadm -C /dev/md3 --bitmap=internal -l 5 -n 5 /dev/sdc1 /dev/sdd1 >> /dev/sde1 /dev/sdf1 /dev/sdg1 >> What I expect: since the first and the second drive are 1.5 TB size the >> third fouth and fifth drive are treated like 2*1.5 TB, creating a 4.5 TB >> RAID. > Lolwhat. Hey, there is a reason why I ask, no need to lol. >> What would really be created: I know here are people that know and not >> guess : ). > 5x1TB RAID5. Lowest common device size across all RAID members is utilized in > an array. > > But what you do after that, is you also create a separate 2x0.5TB RAID1 from > the 1.5TB drives' "tails", and join both arrays into a single larger volume using LVM. > > The result: 4.5 TB of usable space, with one-drive-loss tolerance (provided by > RAID5 in the first 4 TB, and by RAID1 in the 0.5TB "tail"). Thanks for clearing that up. I probably would have noticed when trying in a few weeks, but knowing beforehand helps. To make you lol more, following would work too: Use only 750GB partitions, use the 3*250 GB loss at the end of each 1 TB drive for the fourth 750 GB, and RAID6 those 8*750. Result is 4.5 TB with a one-drive-loss tolerance and really bad performance. I spare you the 500 GB partitions example which result in 4.5 TB with a one-drive-loss tolerance and really bad performance. Jou