From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Janos Haar" Subject: Re: questions about softraid limitations Date: Thu, 15 May 2008 01:29:57 +0200 Message-ID: <01be01c8b61a$6e616260$9300a8c0@dcccs> References: <002801c8b55a$60e4a360$0404a8c0@dcccs> <482AC2BB.5010602@dgreaves.com> Mime-Version: 1.0 Content-Type: text/plain; format=flowed; charset="iso-8859-2"; reply-type=original Content-Transfer-Encoding: 7bit Return-path: Sender: linux-raid-owner@vger.kernel.org To: David Greaves Cc: linux-raid@vger.kernel.org List-Id: linux-raid.ids Hello David, ----- Original Message ----- From: "David Greaves" To: "Janos Haar" Cc: Sent: Wednesday, May 14, 2008 12:45 PM Subject: Re: questions about softraid limitations > Janos Haar wrote: >> Hello list, Neil, > > Hi Janos > >> I have worked on a faulty hw raid card data recovery some days before. >> The project is already successfully done, but i run into some >> limitations. > > Firstly, are you aware that Linux SW raid will not understand disks > written by > hardware raid. Yes, i know, but the linux raid is a great tool to try it, and if the user know what he is doing, it is safe too. :-) > >> Than try to build an "old fashion" linear arrays from each disks + 64k >> another blockdevice. (for store the superblock) >> But the mdadm refused to _build_ the array, because the source scsi >> drive is jumpered to readonly. Why? :-) > This will not allow md to write superblocks to the disks. I think exactly for this steps: dd if=/dev/zero of=suberblock.bin bs=64k count=1 losetup /dev/loop0 superblock.bin blockdev --setro /dev/sda mdadm --build -l linear /dev/md0 /dev/sda /dev/loop0 The superblock area is writable. And this is enough to try to assemble the array to do the recovery, but this step is refused. > >> >> I try to build the array with --readonly option, but the mdadm still >> dont understand what i want. (yes, i know, rtfm...) > This will start the array in readonly mode - you've not created an array > yet > because you haven't written any superblocks... Yes, i only want to build, not to create. > > >> Its OK, but what about building a readonly raid 5 array for recovery >> usage only? :-) > That's fine. If they are md raid disks. Yours aren't yet since you haven't > written the superblocks. I only want to help for some people to get back the data. I only need to build, not to create. Thanks, Janos Haar > > > David > > -- > To unsubscribe from this list: send the line "unsubscribe linux-raid" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html