taking advantage of hammer

patric conant mirage.computing at gmail.com
Wed Aug 8 11:08:41 PDT 2018


Without snapshots filesystem operations are not atomic, when you Backup,
copy, sync, rsync, you are not getting a cohesive operation, but the
various states of individual files at the time they are accessed. So, no,
you can't back up UFS, with any sort of guaranteed consistency, yes each
file can be consistent, but for example, the logs for services, and the
file states of those services are out of sync, now when you restore you
have logs that are not for point of time that the files are for.
Snapshotting is pretty much the cornerstone of modern storage.  Next
checksumming, which I'm not aware of UFS support in. Without checksumming
the only source of validity of a file is the file itself. There's no
guarantee or even expectation of file consistency, in traditional file
systems, just that we trust the hardware because we have to. RAID mitigates
this, to the tune of reducing it 50-90%, but an 8TB live data set simply is
not exactly what was laid down on the storage medium, and there's no
expectation of such. That's some of the nitty gritty of the modern storage
layer, but as we all know and experience, systems run for years without
these problems enjoying any sort of remedy outside of best effort, there's
probably machines with massive data-sets, and decades of history, whom have
been subject to these problems, being restored from file-level backups many
times, and having the total of the writes be in the multiple petabytes
range, and the applications running on top seeming no worse for wear. This
speaks to the resiliency to some level of corruption of most applications.

On Tue, Aug 7, 2018 at 6:57 PM Bob Obrien <bobo90210 at protonmail.com> wrote:

> Hello there,
> I am enjoying Dragon Fly BSD so far, nice and snappy, seems sensibly
> organized.
> I like the idea of HAMMER but for my relatively basic uses I am not seeing
> a great benefits. Most notably, PFS seem to be a huge part of the design
> and what makes it tick. OK, cool, I guess you can snapshot via PFS. But
> wait, now you can snapshot ANY directory? mount_null also seems core to a
> basic DF setup but that is not limited to hammer at all. Backups, copies,
> syncs, yes it seems a neat organizational tool but at the same time I copy,
> rsync, etc etc with all my UFS drives and it works great. Assuming small
> enough files and drives that limitations are not being reached, of course.
> Maybe if I was a more advanced sysadmin type I would have more specific
> demands or use cases that would take advantage?
> Or maybe I simply need someone to explain how these benefit me and I will
> see the light, and improve my workflows. Thanks!
> Sent with ProtonMail <https://protonmail.com> Secure Email.

Patric Conant
Mirage Computing Lead Consultant
@MirageComputing <https://twitter.com/MirageComputing>on twitter
316 409 2424
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