From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mircea Ciocan Subject: Re: Please help with a special RAID 1 setup Date: Wed, 07 Jan 2004 22:17:13 +0200 Sender: linux-raid-owner@vger.kernel.org Message-ID: <3FFC6949.1060101@interplus.ro> References: <8075D5C3061B9441944E137377645118012F02@cinshrexc03.shermfin.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <8075D5C3061B9441944E137377645118012F02@cinshrexc03.shermfin.com> To: "Rechenberg, Andrew" Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids Rechenberg, Andrew wrote: > > > > >>-----Original Message----- >>From: linux-raid-owner@vger.kernel.org >>[mailto:linux-raid-owner@vger.kernel.org] On Behalf Of Cress, Andrew R >>Sent: Wednesday, January 07, 2004 9:48 AM >>To: Catalin BOIE; Mircea Ciocan >>Cc: linux-raid@vger.kernel.org >>Subject: RE: Please help with a special RAID 1 setup >> >> >>Note that RAID-1 will only ever have a maximum of 2 active disks. >> >> > >I don't believe that the above is a correct statement. Linux software >RAID1 will allow mirroring across more than 2 devices: > >[root@cinshrlnxlap01 ~]# cat /proc/mdstat >Personalities : [raid1] >read_ahead 1024 sectors >md2 : active raid1 [dev 01:02][2] [dev 01:01][1] [dev 01:00][0] > 4032 blocks [3/3] [UUU] > > > This is a refershing info, depressing is the fact that a slice can't be added unobrtusively ( sp ?), I'll try Luca's solution first than scratch & rebuild if this will be a resounding failure ;). [SNIP] >We had a "triple" mirror sofware RAID setup on a box as a "poor man's >snapshot" before we started using LVM. We triple mirrored and then >broke one mirror to backup and then added the removed disk back into the >array and re-synched. LVM snapshots are much more elegant and LVM >provides more functionality such as extended volumes when you want to >add more space. You have to be careful using LVM because as of 2.4.18 >there was a Linux VM bug that would not allow snapshotting with greater >than about 6GB of system RAM. > >However, I would recommend recreating the filesystem on top of LVM and >using snapshots to accomplish what you want. We use LVM on top of SW >RAID with great success. > > > Ha, so I'm not the only one crazy enough to propose such a solution, I'm happy that I'm not alone :), did it worked ?? I belive that was designed and initialised from the first time as a 3 slice raid, the 3rd slice wasn't aded as an aftertought ?? The raid boxes have 4GiB RAM so is not a problem, BTW to you have a pointer for starting the RTFM about that LVM and especially those snapshots, is there a posibility to to save the inital setup with 2 slices or everything has to be destroyed and recreated again??? Best regards, Mircea