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

No you are confused pvs are created on disk partitions, one or more pvs then make you vg.

LVs are created on top of VGs, VGs are created on top of PVs, PVs are created on partitions on block devices or whole block devices.

(Ok we shall stop here however blocks devices could be loop back, meta devices like raid 0/1/5 etc hardware/software or real disks however that is not LVM any more.)

Ok, i think I get it now. At the minute, my vg (vg0) only has on PV in it (/dev/md3 which you can tell is a mdadm RAID device). I wasn't aware you could add more PVs (that's pretty cool!). So, let's say I had a spare partition (/dev/hdb7 as an example). To my vg0 volume group, I would firstly:

pvcreate /dev/hdb7
vgextend /dev/hdb7

Then, every time I create a new customer LV, I would do:

lvcreate -nNewCustomerLV -L20G vg0 /dev/md3

Then, every time I wanted to create a snapshot:

lvcreate -L20G -s -n data_snap /dev/vg0/NewCustomerLV /dev/hdb7

Is that correct? No Leakage? And no zeroing needed?

Side note: Since I didn't partition my servers with this in mind, my new PV will probably have to be an iSCSI device located on a remote target :( Either that or use a loopback device with an image, but I'd be scared that the system would not boot properly. Can you give me any tips on how to use an image file as a PV just for snapshots?


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