A question which came up again on irc last night was whether an existing filesystem on a non-LVM partition can be turned into an LVM logical volume without having to wipe the disk. With LVM2, I think the answer is often 'Yes'. N.B. These instructions are untested. Perhaps someone would be interested in trying them out and turning them into a script? LVM2 needs to use for itself just one sector on the device (for a label). By default this is the second sector - ext2 and ext3, for example, don't use this sector. But some bootloaders might - check first. You'll also need at least one other normal physical volume in your volume group to hold the LVM2 metadata. Not a problem if the reason for the exercise is to expand the filesystem! But it could be quite small. Say the existing filesystem is on /dev/sda1. 1. Run: pvcreate -M2 --metadatacopies 0 -Zn /dev/sda1 Do *not* miss the '-Zn' or you will wipe some of your data! -M2 is unnecessary if it's the default. This command generates an LVM2 label and writes it into the second sector. 2. If you're using an existing volume group, skip this step. Otherwise create the second PV in the normal way. Say it's /dev/sdb (not partitioned). Run: pvcreate -M2 --metadatacopies 1 /dev/sdb -M2 is unnecessary if it's the default. --metadatacopies 1 is unnecessary if it's the default. (You can also use 2 but not 0.) 3. Determine the actual size of your existing filesystem, the actual size of the disk or partition holding your filesystem and choose a suitable physical extent size for the volume group. The size of your new LV will be an exact multiple of this physical extent size and needs to be at least as large as the filesystem. The size of your new LV needs to be no larger than the actual size of the disk or partition that holds the filesystem. Disk/partition size >= New LV size >= filesystem size In the example here, I'm going to use 4k, but normally you'll be able to use a much larger size and you should do so. You can use 'pvs -o+dev_size' to display the device size and use --units to do divisions for you (see man page). If you're using an existing volume group, use vgchange -s to reduce the physical extent size if necessary and then run vgextend to add /dev/sda1 to it. Otherwise create a new volume group. Let's say the volume group is called vg0. vgcreate -M2 -s 4k vg0 /dev/sdb /dev/sda1 -M2 is unnecessary if it's the default. Let's say you've calculated that the number of PEs in your new LV will be 2000. 4. Now the part we don't yet have a tool option for. [This should be handled with a new vgcreate/vgextend parameter that sets pe_start to 0 and does the necessary calculations.] Edit /etc/lvm/backup/vg0 (generated by the vgcreate or the vgextend). Find the physical volume section for /dev/sda1 and reduce pe_start to 0 and increase pe_count to the number of physical extents you decided you needed for your new LV in step 3, 2000 in this example. (Typically you'll need to add the original value of pe_start divided by pe_size expressed in 512 byte sectors). Apply your revised backup file with 'vgcfgrestore vg0'. 5. Create your new logical volume. Important: don't forget -Zn or you'll wipe the start of your filesystem! lvcreate -Zn -l2000 vg0 /dev/sda1 6. Finally run fsck on your new logical volume and check everything worked. Alasdair -- agk@redhat.com _______________________________________________ linux-lvm mailing list linux-lvm@redhat.com https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
