From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mx1.redhat.com (ext-mx03.extmail.prod.ext.phx2.redhat.com [10.5.110.27]) by int-mx09.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id tA8Hm8ue006546 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO) for ; Sun, 8 Nov 2015 12:48:08 -0500 Received: from bugzy.highpoweredhelp.com (173-165-161-162-atlanta.hfc.comcastbusiness.net [173.165.161.162]) by mx1.redhat.com (Postfix) with ESMTP id A24E18E50E for ; Sun, 8 Nov 2015 17:48:07 +0000 (UTC) Received: from ABRAHAM.highpoweredhelp.local (highpoweredhelp.com [173.165.161.161]) by bugzy.highpoweredhelp.com (Postfix) with ESMTPS id 323A81DA9 for ; Sun, 8 Nov 2015 12:38:33 -0500 (EST) Received: from [IPv6:::1] (localhost [IPv6:::1]) by d7.highpoweredhelp.local (Postfix) with ESMTP id 3A1411E0187 for ; Sun, 8 Nov 2015 12:41:20 -0500 (EST) Message-ID: <563F8940.3020706@highpoweredhelp.com> Date: Sun, 8 Nov 2015 12:41:20 -0500 From: Michael Munger MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Subject: [linux-lvm] dd on a lv? Reply-To: LVM general discussion and development List-Id: LVM general discussion and development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , List-Id: Content-Type: text/plain; charset="us-ascii" To: linux-lvm@redhat.com In preparing a lv for LUKS, I wanted to write random data to the entirety of the logical volume. (It's one of two lv's in the vg that are running LUKS, the other lv are not encrypted, and all reside on the same pv, which is a linux-raid (mdadm) device at /dev/md0). I used dd if=/dev/urandom of=/dev/mygroup/mylogicalvolume to write random data to the entirety of the lv device. Here's the issue: The lv is only 4TB (yes... this took days). I had estimated it would stop some time early this morning. This afternoon when I checked it, dd had claimed to have written 4.2 TB of data to a 4TB device. I immediately thought: "How's that possible" and began to worry that it escaped the logical volume and began to write other areas of the array. But, dd if=/dev/mygroup/othervol1 bs=1K count=1 | hexdump -C showed a LUKS header (as it should) and the same command on the other lv showed the proper header as well. I took this to mean that those lv's were in tact. How is it possible that I can write 4.2TB to a 4.0 TB logical volume? Should I be worried that I have somehow overritten something somewhere else? If so, how do I find and check that? (I have backups, so if I need to restore, I need to do it now). P.S. When I did this on the other lv, which is only 100GB, dd behaved as expected, and wrote only 100GB of random data to the logical volume. -- Michael Munger, dCAP, MCPS, MCNPS, MBSS High Powered Help, Inc. Microsoft Certified Professional Microsoft Certified Small Business Specialist Digium Certified Asterisk Professional michael@highpoweredhelp.com