<div>On 9/23/08, Peter A. Castro <<a href="mailto:doctor@fruitbat.org">doctor@fruitbat.org</a>> wrote: <blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0px 0px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid">On Tue, 23 Sep 2008, Larry Dickson wrote: <blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0px 0px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid">Hi Bob, Notes interpolated. On 9/23/08, Peter A. Castro <<a onclick="return top.js.OpenExtLink(window,event,this)" href="mailto:doctor@fruitbat.org" target="_blank">doctor@fruitbat.org</a>> wrote: <blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0px 0px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid"> On Tue, 23 Sep 2008, Bob Bell wrote: Greetings, Bob, I'm up a creek, and hoping someone out there can help rescue my data, or at <blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0px 0px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid">least tell me what went wrong so that I don't have a repeat event. I'm starting with this question on linux-lvm, though let me know if you think the discussion needs to be on linux-raid as well. I'm setting up a new server running Ubuntu's Hardy Heron release. `lvm version` reports: LVM version: 2.02.26 (2007-06-15) Library version: 1.02.20 (2007-06-15) Driver version: 4.12.0 `uname -a` reports: Linux sherwood 2.6.24-16-server #1 SMP Thu Apr 10 13:58:00 UTC 2008 i686 GNU/Linux I initially created an md RAID5 device with only two components (matching 320 GB SATA HDDs). </blockquote> </blockquote>This is puzzling, since by the usual definition, there is no such thing as a 2-disk RAID5. Your description of its virtual size indicates it is a RAID1, or equivalent. </blockquote> While it's unusual to have only 2 disks in a "RAID5" (usally you want 3 drives min), it is possible, if unreliable (can you say "half-of-a-mirror" ?)</blockquote> <div> </div> <div>If you are meaning a degraded 3-disk RAID5, then he should have had a virtual size of 640GB. He reported 320GB which would be the value expected of a RAID1. You can apply the RAID5 algorithm to 2 disks, but then you just get the equivalent of a RAID1, since a parity sector made so the XOR sum of it and ++ one ++ data sector is zero must equal that data sector.</div> <div> </div> <div>Larry</div> <blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0px 0px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid"> <blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0px 0px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid"> I created a single Physical Volume using the entirety of that md device <blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0px 0px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid"> <blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0px 0px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid">(320 GB), and then created several Logical Volumes for different filesystems (all ext3). This was done using the Ubuntu installer. After installing I used lvresize to increase the size of a few of the Logical Volumes, as I was conservative regarding the size during installation. These filesystems hold data that is not a critical part of the system (mail, music, video, etc.). </blockquote> </blockquote>The LVs live atop the virtual md device so this should not have done anything essentially disturbing. </blockquote> Yep, I have several VG's with LV's on top a several MDs without any trouble. <div> <blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0px 0px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid"> (I also have a similar setup with a couple of IDE drives that I use for the <blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0px 0px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid"> <blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0px 0px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid">system (/home, /var, /boot, /), but I haven't touched those since the install and they continue to work fine.) I then copied data from a third matching 320 GB SATA HDD to one of the Logical Volume filesystems on the md device. After freeing up that drive (by relocating its contents to the LVM/MD setup), I added the drive to the md device, which brought the total to 2 active devices and 1 spare device. I then grew the number of devices to 3 and waited for the reshape to finish (increasing the capacity to 640 GB). </blockquote> </blockquote> If this is a reshape in md, then LVM should have seen nothing (since the 320 GB it knew about should still be there). I bumped the values in /proc/sys/dev/raid/ so that I wouldn't have to <blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0px 0px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid"> <blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0px 0px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid">wait as long. </blockquote> My understanding of RAID5 is that once you configure the set of disks to the array, you can't just add an additional disk to it. Attempting to do so does more than just "reshape" the array, it changes the logical layout of the sectors completely. It's no wonder that LVM can't find anything, since it's data (if it survived the reorg) is no longer where it should be. And, once you've done this, there's really no going back to recover. This is assuming my understanding of RAID5 is correct. </blockquote> I disagree, because assuming the md reshape operates intuitively, the old 320 GB of data should still be visible as the first 320 GB of data on the new VIRTUAL 640GB device. And LVM should know nothing about the underlying RAIDing, so it should be happy to look there. However, I have no idea what "bumped the values in /proc/sys/dev/raid/" means, or if it causes LVM to look in the wrong places for things. </blockquote> </div>I don't believe the MD/RAID5 operates in this way. He started with a 2-disk RAID5 (effectively having the data logically interleaved between the two drives), then he added an additional disk. The way RAID works, it doesn't just add the disk space to the end of the array (that would not create a recoverable scenario should it or one of the others fail), it re-integrates and effectively re-interleaves the logical sectors to re-spread the data across all three drives. The trouble is, I don't think you can actually do this with current MD tech (I could be wrong). Perhaps a better question would be to ask how, exactly, Bob create his array initially (what commands) and what steps he took to add the new drive (again, what commands did he issue). That would give us a better idea of how the array looked before and after. All of this is orthogonal to LVM, however. I suspect a RAID/MD email list would be a better forum to discuss this. <div> <blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0px 0px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid">Larry Dickson Cutting Edge Networked Storage Now that the reshaping is completed, LVM can't find the physical volume on <blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0px 0px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid"> <blockquote class="gmail_quote" style="PADDING-LEFT: 1ex; MARGIN: 0px 0px 0px 0.8ex; BORDER-LEFT: #ccc 1px solid">that device anymore. I tried rebooting the system, but the problem remained. Checking /proc/mdstat shows that the md device is up and healthy. The pvdisplay command only shows my other Physical Volume (for the IDE drives). I found the pvck command and ran that on the md device, and it states that there is no LVM label on the device. It is my understanding that the steps I outlined should have worked. I planned to follow them with pvresize, then lvresize, then umount, resize2fs, and mount again. I've seen this procedure outlined a few different places, including at <a onclick="return top.js.OpenExtLink(window,event,this)" href="http://gentoo-wiki.com/Resize_LVM2_on_RAID5" target="_blank">http://gentoo-wiki.com/Resize_LVM2_on_RAID5</a>. Did I do something wrong? Is there anyway to rescue my data? I saved the contents of /etc/lvm/backup/ when I noticed the problem -- perhaps that might help? If there's no way of saving the data, I'd at least like to figure out what happened in the first place. Thank you. Your thoughtfulness and help is appreciated. </blockquote> -- Peter A. Castro <<a onclick="return top.js.OpenExtLink(window,event,this)" href="mailto:doctor@fruitbat.org" target="_blank">doctor@fruitbat.org</a>> or <<a onclick="return top.js.OpenExtLink(window,event,this)" href="mailto:Peter.Castro@oracle.com" target="_blank">Peter.Castro@oracle.com</a>> "Cats are just autistic Dogs" -- Dr. Tony Attwood _______________________________________________ linux-lvm mailing list <a onclick="return top.js.OpenExtLink(window,event,this)" href="mailto:linux-lvm@redhat.com" target="_blank">linux-lvm@redhat.com</a> <a onclick="return top.js.OpenExtLink(window,event,this)" href="https://www.redhat.com/mailman/listinfo/linux-lvm" target="_blank">https://www.redhat.com/mailman/listinfo/linux-lvm</a> read the LVM HOW-TO at <a onclick="return top.js.OpenExtLink(window,event,this)" href="http://tldp.org/HOWTO/LVM-HOWTO/" target="_blank">http://tldp.org/HOWTO/LVM-HOWTO/</a> </blockquote> </blockquote> -- Peter A. Castro <<a onclick="return top.js.OpenExtLink(window,event,this)" href="mailto:doctor@fruitbat.org" target="_blank">doctor@fruitbat.org</a>> or <<a onclick="return top.js.OpenExtLink(window,event,this)" href="mailto:Peter.Castro@oracle.com" target="_blank">Peter.Castro@oracle.com</a>> "Cats are just autistic Dogs" -- Dr. Tony Attwood</div> _______________________________________________ linux-lvm mailing list <a onclick="return top.js.OpenExtLink(window,event,this)" href="mailto:linux-lvm@redhat.com">linux-lvm@redhat.com</a> <a onclick="return top.js.OpenExtLink(window,event,this)" href="https://www.redhat.com/mailman/listinfo/linux-lvm" target="_blank">https://www.redhat.com/mailman/listinfo/linux-lvm</a> read the LVM HOW-TO at <a onclick="return top.js.OpenExtLink(window,event,this)" href="http://tldp.org/HOWTO/LVM-HOWTO/" target="_blank">http://tldp.org/HOWTO/LVM-HOWTO/</a> _______________________________________________ linux-lvm mailing list <a onclick="return top.js.OpenExtLink(window,event,this)" href="mailto:linux-lvm@redhat.com">linux-lvm@redhat.com</a> <a onclick="return top.js.OpenExtLink(window,event,this)" href="https://www.redhat.com/mailman/listinfo/linux-lvm" target="_blank">https://www.redhat.com/mailman/listinfo/linux-lvm</a> read the LVM HOW-TO at <a onclick="return top.js.OpenExtLink(window,event,this)" href="http://tldp.org/HOWTO/LVM-HOWTO/" target="_blank">http://tldp.org/HOWTO/LVM-HOWTO/</a> </blockquote></div>