Re: [9fans] A potentially useful venti client

[Steven Stallion <sstallion@gmail.com>]

I have a similar setup. On my file server I have a mirrored pair of
high-endurance SSDs tied together via devfs with two fossil file
systems: main and other. main is a 32GB write cache which is dumped
each night at midnight (this is similar to the labs configuration for
sources). other is the remaining 96GB for data that doesn't need to
survive if both SSDs happen to fail at the same time.

My venti store is run on a large Linux machine (~6TB of RAID6 storage)
and is served via plan9port. Another highly recommended setup is if
you happen to have a Coraid EtherDrive (I'm biased towards the SRX
line) this make fantastic stores via the magic of AoE. Unfortunately I
don't have the rack space, otherwise I'd be using one of those
instead.

If you're curious about the venti-on-linux setup, I have some scripts
and a README posted on sources:
https://9p.io/magic/webls?dir=/sources/contrib/stallion/venti

Somewhat more recently, I wrote a collectd client for plan9 and I also
monitor my file server using nagios. If there's any interest, I'd be
happy to post those sources as well.

Cheers,
Steve

On Tue, Dec 12, 2017 at 2:15 PM, Steve Simon <steve@quintile.net> wrote:
> Re: fossil
>
> Fossil must not fill up, however I would say that the dropoff was the lack of clear
> documentation stating this.
>
> Fossil has two modes of operation.
>
> As a stand alone filesystem, not really intented (I believe) as a production
> system, more as a replacement for kfs - for laptops or installation systems.
>
> A full fossil system is when it is combined with a local venti (venti on the same
> machine or on a fast, low latency network connection). Here most files are pulled
> from venti (in the limit fossil only contains a single score which redirects the root
> of the filesystem to a venti score. However as you change files the new version
> is stored on fossil.
>
> Every night aty 4 or 5 am (by convention) fossil does a snap, bumps it epoch which
> marks all the changed files as readonly and further changes creates a new file.
> The readonly files are then written to venti in the background and their space in fossil
> reclaimed.
>
> This means the fossil only needs to be big enough to contain all the changes you
> are likely to make in a day - in reality 10Gb or fossil will never fill up unless
> you decide to archive your entire dvd collection on the same day.
> I have been running fossil and venti since 2004. Fossil did have problems doing
> ephemerial dumps (short lived dumps every 15 mins which live for a few days).
> This bug used to cause occasional fossil crashes but venti never lost a byte.
>
> The bug was fixed before the labs froze and fossil has been solid since.
>
> I used an ssd for venti which helps its performance, though even with this it will
> never match liniux filesystem performance (cwfs may well do better), but I know it
> and its fast enough for me for now.
>
> -Steve
>