zfs q regarding backup strategy
dpchrist at holgerdanske.com
Fri Oct 1 19:53:23 UTC 2021
On 10/1/21 07:14, tech-lists wrote:
> On Thu, Sep 30, 2021 at 08:06:28PM -0700, David Christensen wrote:
>> Michael Warren Lucas is my go-to author for FreeBSD and ZFS:
> I think those were written quite a while ago? I need something covering
> both the old zfs and OpenZFS. I'm looking for the differences, any
> incompatibilities that might apply in my context. It'd be great if he
> has more recent stuff.
I find MWL's writings to be recent enough. He updates his books. I
expect he has a process for updating blog posts.
>> I use zfs-auto-snapshot for snapshot creation/ management, and homebrew
>> commands/ scripts for replication. The homebrew stuff is problematic.
> yeah homebrew I'm trying to avoid for lots of reasons.
>> I need to evaluate something like zfs-replicate (available as a FreeBSD
>> package of the same name):
> Thanks for the suggestion. Problem with zfs-replicate is its dependence
> on python, which from what I've observed historically, is a bit of a mess.
> On my desktop there's lots of ports still needed that are dependent on
> python2 even though upstream have retired it. They show up in
> reports as EoL'd due to python2; there's loads right now and the desktop
> builds its ports in poudriere weekly.
Thankfully, I can find what I need in packages; and zfs-replicate is a
> What I'm looking for is something (ideally) written in sh. Or even perl.
Available in the links I already posted.
> But even before that, need to understand incremental backups properly.
I learned by beating my head against the console. :-/
> Basically the backup needs to be (effectively) write-only. By that, I
> mean only added to.
ZFS snapshots are read-only by design.
When you replicate a read-write filesystem, you replicate via snapshots.
The snapshots arrive read-only, and the filesystem arrives read-write.
If you touch the destination filesystem, the next incremental
replication will fail. The '-F' option to 'zfs receive' is required to
discard changes on the destination.
I do not see an option for 'zfs receive' to set properties during
replication, but you could write a script to set 'readonly=on' on the
destination after replication. If so, I don't know what happens on the
next incremental replication -- properties are overwritten? Replication
fails? Testing is required.
Eventually, the destination will fill up. Choices include replacing the
media and deleting snapshots. I do the latter (by hand).
> Maybe zfs snapshots aren't the way to go;
Snapshots and replication are killer features of ZFS, and primary
reasons why I use ZFS.
> maybe rsync in the backup
> direction only (apart from when something needs to be restored) would
> suit my context better.
I use rsync(1) to backup from non-ZFS sources to ZFS.
> What do you think?
"More than enough rope to shoot yourself in the foot".
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