On Sun, 6 May 2007, Scott Lamb wrote: > Date: Sun, 6 May 2007 13:47:28 -0700 > From: Scott Lamb <slamb at slamb.org> > Reply-To: CentOS mailing list <centos at centos.org> > To: CentOS mailing list <centos at centos.org> > Subject: Re: [CentOS] Re: LVM Resizing Problem > > On May 6, 2007, at 8:14 AM, Ross S. W. Walker wrote: > >> LVM even warned you --IN CAPS-- "THIS MAY DESTROY YOUR DATA". > >> I guess it was right. I haven't had much luck with reducing a > >> volume below its > >> initial size. I usually make a new LV and rsync or cp -a the > >> data over to it. > >> I try to leave some free space just for this. Or add a drive > >> temporarily. > > > > Were the LV calculations done in the VG's extent size unit? > > > > Most people forget LVM rounds to the closest whole extent in it's > > calculations which I believe is 4MB by default, so care must be > > taken to make sure any file system fits comfortably in there > > first. > > Is there any tool which is aware of both the filesystem and LVM > layers and can correctly ensure the filesystem fits? no tool as such I am aware of, but bc is your good friend. Use lvdisplay rather than lvs, pvdisplay,. etc and count in LE (logical extents) rather than MB or GB. > > The filesystem on my only large disk array is corrupt, presumably due > to some problem in one of the Fedora Core 6 update kernels. I > rebooted into single user mode, fscked (which found a huge number of > errors) and rebooted and it's still complaining. So it's time to > start over with a fresh filesystem on a more trustworthy dom0 system > (CentOS 5). I don't have anything vital stored only there, but there > are a number of large files I'd like to save if possible. They don't > fit anywhere else. > > Here's my plan: > > 1. boot a CentOS 5 DVD in rescue mode, fsck the filesystem again > 2. shrink the existing filesystem and LV (crossing my fingers) You canno shring ext3 until it fsck clean, as far as I remember. > 3. install CentOS 5 to a new LV and filesystem > 4. copy whatever's left of these files > 5. delete the old LV > 6. expand the new filesystem and LV > > Never done steps #2 and #6 before, and I want to give it as much > chance of success as possible with an already-screwed-up filesystem. I would suggest you to add external HDD (e.g. USB2, or IDE/SATA with USB2/PATA+SATA converter) and copy your data. If the filesystem is screwed up, resizing can only make its state worse. > I see the section in the LVM HOWTO [1], but it doesn't mention the > sort of gotcha you're describing. I'm skeptical of LVM's > documentation in general. It doesn't even mention RAID (md), instead > including some incredibly stupid recipes virtually guaranteed to lose > all your data when one disk out of many fails [2]. Could you please elaborate or give some pointers about reasons for those recipes being stupid, etc. ? > > [1] - http://www.tldp.org/HOWTO/LVM-HOWTO/reducelv.html > [2] - http://www.tldp.org/HOWTO/LVM-HOWTO/recipeadddisk.html > > Cheers, > Scott > >