getting started with lvm

[curmudgeon]

While it seems there are a number of wonderful tutorials out there for setting up lvm on the operating system drive, I haven't quite seen any that explained how to do what I want.

Let's suppose I have a 1 TB hard drive for data only (nothing to do with the os).

I want to combine relative small parts (say 32 GB) into three or four pools of storage (that I can create and delete), and be able to reassign the 32 GB parts from one pool to another.

So first of all, I assume I have to create approximately thirty 32 GB partitions before I begin. Is that correct?

How do I create and delete the storage pools?

How do I assign (and unassign) a partition to a particular pool?

Thank you in advance.

[kwesadilo]

When you say pools of storage, do you mean a pool that would be used for a single filesystem or for multiple filesystems? The former would be a logical volume, and the latter would be a volume group. Since putting multiple filesystems/logical volumes on one disk partition is well-covered elsewhere, I take it you mean you want multiple volume groups, i.e. independent storage pools, on one disk partition, and you want to be able to move physical storage between those pools. As a caveat, I can't think of a good reason that you would do this, and what I'm about to describe is tedious and horrible and somewhat defeats the purpose of having LVM. But here is what I would do:

1. Create like 300 32-GB partitions on your 1-TB HDD
   
2. Make each of those partitions a pv using pvcreate
   
3. Use vgcreate to create three or four volume groups, dividing the PVs up between them to suite
   
4. Use lvcreate to create whatever logical volumes you want in each of the volume groups
   
5. When you decide that you want to move a PV between VGs, use pvmove to move any data on that PV to other PVs in the same VG, then use vgreduce to remove that PV from the VG. Then use vgextend to add the PV to another VG.
   
6. During the preceding process make whatever adjustments are necessary for your filesystem and LV sizes to ensure that no filesystem is larger than the LV that contains it.
   

That seems very labor-intensive and error-prone to me. I suspect you'd be much happier making one PV for your whole drive and one VG over that and then making several LVs for your different filesystems and resizing them as needed.

[szatox]

yes, just create one partition on phisical drive, create phisical volume on it, create volume group with this phisical volume and then create as many logical volumes as you need at the moment (then create filesystems on them as you would do with any other partition without lvm). You can add more logical volumes later, or resize existing volumes - just make sure filesystem never is bigger than lv it resides on or you WILL lose some data - as long as you have unsused space. And when you need more space, you can buy another phisical drive, plug it, create phisical volume on it and.... add it to existing volume group which allows you even creating logical volumes bigger than any of the disks you have plugged in.
There are a lot of good howtos on what command to use and with what parameters.

Now, if you needed multiple volume groups, you would know you need it, and you would kow lvm well enough not to ask this question, so don't bother with creating 300 partitions and a dozen of volume groups. 1 partition for lvm per phisical drive is enough, and 1 volume group for all your phisical and logical volumes.
I don't think you can boot from lvm though, so if you wanted to ever have root on lvm you must make separate /boot partition that will be accessed directly rather than by lvm - since you were talking about data storage space it's not likely your concern right now, but it's good to know anyway for when you change your mind.

maybe i'm chaotic right now, but I remember i was a bit puzzled with design of LVM stack at first, so here's a littlle thing to help grasp the concept:
pv is a device or partition that actualy stores data
lv is a name for a piece of space you want to access, making it effectively a partition you mount and use
vg is a way to merge all space from all pvs you have added to it and atcs as a big hard drive you can repartition at any time to add, delete or resize lvs - and it's easy t omanage since you request a partition of given size rather than starting at sector X and ending at sector Y. You don't care where it starts, you order some amount of space and you get it.

[curmudgeon]

Thanks for the replies (sorry I didn't notice them sooner).

[vaxbrat]

Seeing as how you might consider something other than lvm (ie zfs pools), you will also want to look at btrfs subvolumes. Unlike zfs, you can selectively enable automatic compression depending on what you think the data will allow. If you need to spread redundant copies of objects around on separate physical drives, look at running ceph on top of btrfs.

[khayyam]

[curmudgeon]

[khayyam]

[curmudgeon]

[khayyam]

[curmudgeon]

[khayyam]

[frostschutz]

[curmudgeon]

Let me give a simple case of a problem that whatever method I choose must handle.

Suppose I have two storage pools (call them hatfield and mccoy).

Suppose I need more storage in mccoy, and want to obtain that storage by shrinking hatfield.

Obviously, I need to sanitize (clear and validate) the media after removing it from hatfield, and before adding it to mccoy (see NIST SP 800-88, NSA 130-1 and DoD 5220.22-M).

With separate physical partitions, this is trivial (remove the partitions from hatfield, shred them, verify that they are zeroed out, recreate them, and add them to mccoy).

I don't see how this is possible giving a volume manager control over a single partition hard drive. Maybe there is a way to do this using that method (and maybe, in fact, it is just as easy, if not easier). If this can be done, please enlighten me as to how. I will state again that security is the primary (and secondary, and tertiary) concern(s).

[frostschutz]

shred works happily with Logical Volumes.

shred existing logical volume:

[curmudgeon]