1.1. | I have LVM 1 installed and running on my system. How do I start using LVM 2? |
Here's the Quick Start instructions :)
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1.2. | Do I need a special lvm2 kernel module? |
No. You need device-mapper. The lvm2 tools use device-mapper to interface with the kernel and do all their device mapping (hence the name device-mapper). As long as you have device-mapper, you should be able to use LVM2. | |
1.3. |
I get errors about
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The primary cause of this is not having run the “dmsetup mknodes” after rebooting into a dm capable kernel. This script generates the control node for device mapper.
If you don't have the “dmsetup mknodes”,
don't despair! (Though you should probably upgrade to
the latest version of device-mapper.) It's pretty easy
to create the
You should be all set now! | |
1.4. | Which commands and types of logical volumes are currently supported in LVM 2? |
If you are using the stable 2.4 device mapper patch from the lvm2 tarball, all the major functionality you'd expect using lvm1 is supported with the lvm2 tools. (You still need to remove snapshots before upgrading from lvm1 to lvm2) If you are using the version of device mapper in the 2.6 kernel.org kernel series the following commands and LV types are not supported:
The beginnings of support for these features are in the unstable device mapper patches maintained by Joe Thornber. | |
1.5. | Does LVM 2 use a different format from LVM 1 for it's ondisk representation of Volume Groups and Logical Volumes? |
Yes. LVM 2 uses lvm 2 format metadata. This format is much more flexible than the LVM 1 format metadata, removing or reducing most of the limitations LVM 1 had. | |
1.6. | Does LVM 2 support VGs and LVs created with LVM 1? |
Yes. LVM 2 will activate and operate on VG and LVs created with LVM 1. The exception to this is snapshots created with LVM 1 - these should be removed before upgrading. Snapshots that remain after upgrading will have to be removed before their origins can be activated by LVM 2. | |
1.7. | Can I upgrade my LVM 1 based VGs and LVs to LVM 2 native format? |
Yes. Use vgconvert to convert your VG and all LVs contained within it to the new lvm 2 format metadata. Be warned that it's not always possible to revert back to lvm 1 format metadata. | |
1.8. | I've upgraded to LVM 2, but the tools keep failing with out of memory errors. What gives? |
One possible cause of this is that some versions of LVM 1 (The user that reported this bug originally was using Mandrake 9.2, but it is not necessarily limited to that distribution) did not put a UUID into the PV and VG structures as they were supposed to. The most current versions of the LVM 2 tools automatically fill UUIDs in for the structures if they see they are missing, so you should grab a more current version and your problem should be solved. If not, post to the linux-lvm mailing list | |
1.9. | I have my root partition on an LV in LVM 1. How do I upgrade to LVM 2? And what happened to lvmcreate_initrd? |
Upgrading to LVM 2 is a bit trickier with root on LVM, but it's not impossible. You need to queue up a kernel with device-mapper support and install the lvm2 tools (you might want to make a backup of the lvm 1 tools, or find a rescue disk with the lvm tools built in, in case you need them before you're done). Then find a mkinitrd script that has support for your distro and lvm 2. Currently, this is the list of mkinitrd scripts that I know support lvm2, sorted by distro: mkinitrd scripts with lvm 2 support
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1.10. | How resilient is LVM to a sudden renumbering of physical hard disks? |
It's fine - LVM identifies PVs by UUID, not by device name. Each disk (PV) is labeled with a UUID, which uniquely identifies it to the system. 'vgscan' identifies this after a new disk is added that changes your drive numbering. Most distros run vgscan in the lvm startup scripts to cope with this on reboot after a hardware addition. If you're doing a hot-add, you'll have to run this by hand I think. On the other hand, if your vg is activated and being used, the renumbering should not affect it at all. It's only the activation that needs the identifier, and the worst case scenario is that the activation will fail without a vgscan with a complaint about a missing PV. NoteThe failure or removal of a drive that LVM is currently using will cause problems with current use and future activations of the VG that was using it. | |
1.11. | I'm trying to fill my vg, and vgdisplay/vgs says that I have 1.87 GB free, but when I do an lvcreate vg -L1.87G it says "insufficient free extends". What's going on? |
The 1.87 GB figure is rounded to 2 decimal places, so it's probably 1.866 GB or something. This is a human-readable output to give you a general idea of how big the VG is. If you want to specify an exact size, you must use extents instead of some multiple of bytes. In the case of vgdisplay, use the Free PE count instead of the human readable capacity.
Free PE / Size 478 / 1.87 GB
^^^
So, this would indicate that you should do run # lvcreate vg -l478 Note that instead of an upper-case 'L', we used a lower-case 'l' to tell lvm to use extents instead of bytes. In the case of vgs, you need to instruct it to tell you how many extents are available:
# vgs -o +vg_free_count,vg_extent_count
This tell vgs to add the free extents and the total number of extents to the end of the vgs listing. Use the free extent number the same way you would in the above vgdisplay case. | |
1.12. | How are snapshots in LVM2 different from LVM1? |
In LVM2 snapshots are read/write by default, whereas in LVM1, snapshots were only read-only. See Section 8, “Snapshots” for more details | |
1.13. | What is the maximum size of a single LV? |
The answer to this question depends upon the CPU architecture of your computer and the kernel you are a running:
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