[ProgClub programming] top: st : time stolen from this vm by the hypervisor

John Elliot V | ProgClub jj5 at progclub.org
Fri Jun 7 13:52:39 AEST 2019

On 7/6/19 12:49 pm, Roland Turner via programming wrote:
> This is definitely intra-AZ traffic? Why not:
> $ aws ec2 create-snapshot --volume-id {id}

That's actually a really good idea Raz. It turns out the storage costs
for snapshots are $0.055 / GB-month whereas the magnetic provisioned
storage costs are more like $0.08 / GB-month. I hadn't noticed this when
I designed by backup system.

I guess one thing that springs to mind to prefer my current setup to
your suggested approach is a mild concern over vendor lock-in. All other
things being equal I prefer pursuing approaches which would work equally
well if I shifted to another cloud provider... 'rsync' fits that bill,
whereas 'aws' CLI does not.

> This eliminates:
>   * The I/O cost
>   * The network traffic
>   * CPU use by rsync on the source host
>   * The existence of the backup host (depending what else it's doing)
> Yes, you're going to have to do some fiddling to delete snapshots more
> than two hours old. It does not appear straightforward to do it in bash.

Now that I have an incumbent backup system I have to consider changes
through the lens of additional effort per unit cost savings... just with
regard to your notes:

* I/O cost: yes it would eliminate the I/O costs, but those are
manageable at $17/mo

* Network traffic: yes, but that also is manageable at $17/mo.

* CPU use: this is essentially free on both source and target hosts, we
don't need to worry about that

* Backup host: the backup hosts are my Salt Masters, I need to keep them
anyway. I wouldn't need to keep the magnetic disks that are attached
though, and those are $123/mo (although I would pick up some percentage
of that in costs for snapshot storage).

* Fiddling: pursuing your suggestion, which I do agree is potentially a
good approach, would also leave data restores being a little bit fiddly.
At the moment if I need a backed up file I can just SSH in to one of my
backup hosts and find it in the file-system. Restoring/mounting
snapshots is not quite so straight-forward. That is not to say that it's
impossible though, of course.

I think the big saving in pursuing your approach would be the GB-month
storage costs.

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