[linux-lvm] lvm thin provisioning snapshots and btrfs

[Robb Walker]

Also see the same results on ubu 14.04.1 lvm thin provisioning + btrfs. haven't tried arch 3.16 kernel and tools yet

Robb Walker
Linux/Unix Services
Desk (312)542-2361 ~ Mobile (312)804-6034
Email: rwalker at drw.com
DRW Holdings, LLC ~ 540 West Madison St. Chicago, IL 60661


________________________________________
From: linux-lvm-bounces at redhat.com <linux-lvm-bounces at redhat.com> on behalf of Robb Walker <rwalker at DRWHoldings.com>
Sent: Tuesday, September 16, 2014 6:10 PM
To: linux-lvm at redhat.com
Subject: [linux-lvm] lvm thin provisioning snapshots and btrfs

Has anyone used lvm thin prov + btrfs on rhel/cent6u5?


The build I am using off base iso with updates thru end feb 2014 so I have not yet applied all updates. However from rhel alerts I see no specific fixes for lvm or btrfs from that date forward. Unless I missed something.


With lvm thin prov + ext4 I get expected results. When I take a snapshot. I see the snapshot is the state of the lvm volume at the point of time of snapshot creation.


For btrfs, I am using a root subvolume mounted as @foo_root with a thinly provisioned lvm underneath. Same setup just using btrfs.

I take a thin snapshot

lvcreate -n lv_root_thin -s vg_thin/lv_root

snapshot is created

activate with lvchange -Kay  /dev/vg_thin/lv_root_thin


I then mount the snap with mount -odefaults,subvol=@foo_root /dev/vg_thin/lv_root_thin /snaps

The contents match the origin lvm. Both lvms, origin and snap stay in sync with whatever changes I make.

At one point I thought that maybe it was snapping at the subv level so I decided a snapshot of the root vol. However the deletion also appeared in the thin snapshot


Also couple notes:

I never see in lvs that the thin snapshot goes -o- online as I do in ext4

chdir into the /snaps and running df -h . shows that I'm in the snapshot

chdir into /snaps/\@foo_root and running df -h . shows I'm in the origin vol. <this is where I thought it might be snapping at the "raw" brtfs subvolume level


Hopefully this is somewhat clear


Regards and TIA


Robb Walker
Linux/Unix Services
Desk (312)542-2361 ~ Mobile (312)804-6034
Email: rwalker at drw.com
DRW Holdings, LLC ~ 540 West Madison St. Chicago, IL 60661

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