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Re: [linux-lvm] Snapshots and disk re-use

On 06/04/2011 00:39, James Hawtin wrote:
On 05/04/2011 23:19, Jonathan Tripathy wrote:
Excellent point! As long as I use the same PEs for making the snapshot everytime, I don't need to ever erase it (And it can be a nice big size like 50GB, so even my largest customers won't outgrow the snapshot). However though, wouldn't I need to keep the "hog" around just to make sure that the snapshot PEs don't get assigned to a new customer LV in the future (Currently, we don't specify PEs to use when creating normal LVs)?

I think you missed the point of why I suggested using a separate PV, the space could be divided using fdisk it does not have to separate physical disk (This is ok as you will never use this space for mirroring). If snapshots are created on a separate PV you can use pvchange - x n and pvchange -x y to change if it is allocatable and only when you are creating snaps do you make in allocatable that will prevent accidental reuse in customer lvs without lots of hassle. If you don't use pvchange you will need to specify the PVs when ever you create a customer LV.
Ok now things are really getting interesting!

Actually, when I create new customer LVs, I always specify which volume group I want to add it to. E.g:

lvcreate -nNewCustomerLV -L20G vg0

where vg0 is /dev/vg0
and vg0 is a volume group which uses an entire physical partition (Which I guess is called a PV).

Now, if I were to create my snapshots on a seperate vg, eg:

lvcreate -L 20G -s -n data_snap /dev/vg0/NewCustomerLV /dev/vg1

does that mean I never need to use pvchange to "switch off" vg1? And I never need to zero or create a "hog"? And no leakage will ever occur?

Do I get cake now?
Only if it's not a lie.... :)
(Just incase you didn't get the referance http://en.wikipedia.org/wiki/The_cake_is_a_lie)

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