On 12/02/2014 07:11 AM, Shriramana Sharma wrote:
On Tue, Dec 2, 2014 at 6:58 PM, David Sterba <dste...@suse.cz> wrote:
A subvolume is also a snapshotting barrier, so it's convenient to create
subvolumes in well-known paths that contain data that should not be
rolled back (/var/log, /srv, bootloader).
That makes sense. Is there anywhere that the "official" SuSE
recommended subvol layout is mentioned that I can refer to without
having to start up an installer? (I currently chose ext4 for / for
other reasons so I can't refer to my layout.)
There are lots of ways to arrange your system
My preference is to create the snapshots in a super-volume outside of
the normally mounted hierarchy. This simplifies the normal operation of
tools like "locate" which don't understand that the duplicate files from
the snapshot are not interesting. It also means that live operations
(e.g. anything using "find") naturally will not traverse the snapshots
unless the supervolume is mounted explicitly.
I typically call the active root of the system /__System and set it as
the default subvolume to make booting easier.
As in...
mkfs.btrfs /dev/whatever
mount /dev/whatever /mnt
btrfs sub create /mnt/__System
btrfs sub create /mnt/__System/home
btrfs sub set-default (number) /mnt
umount /mnt
mount /mnt
(create OS layout in /mnt)
Then when the snapshotting goes on...
mount -o subvol=/ /dev/whatever /maintenance
SUFFIX=$(date "+_BACKUP_%Y-%M-%d")
cd /maintenance
btrfs sub snap -r __System __System${SUFFIX}
btrfs sub snap -r __System/home __System_home${SIFFIX}
# etc
cd /
umount /maintenance
---
The Real Way™ to think about your active subvolume layouts is to think
about what you really need to preserve and how often.
/home is an obvious candidate for frequent snapshots as it is the place
individual users are most likely to mess up, and it has the most
"irreplaceable" data.
/ (e.g. the semantic system root) [in my example /__System] [not
counting its various subvolumes really only needs backing up before
system software modifications via apt/yumm/portage/wahtever your distro
uses. Or right before you start doing aything "tricky" in /etc
/etc might rate its own subvolume if you are a tinker or your
system-wide configuration needs a lot of motility.
/var tends to have per system configuration stuff
But the real question is "how much complexity of maintenance does the
system _really_ need, and how much of it are you _really_ going to maintain.
The desire to use a feature "just 'cause it's there" should be resisted.
If you are not going to be using the snapshots feature. If you are just
dropping the box in and you are going to ignore it, then don't subvolume
it at all.
You are looking for a balance between the theoretical ideal and the
practical outcome. If you don't know exactly why you are putting the
subvolume in place then it will likely just end up annoying you without
giving any value.
Same for taking and positioning the snapshots.
This is a corollary of the rule that states "A backup script that you've
never done a restore from, should be assumed to be an _unsafe_ or
complete backup, or no backup at all."
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