Re: [9fans] HELP: recoving important header file rudely clobbered by mk

[John Floren <john@jfloren.net>]

On Sat, Jan 29, 2011 at 5:16 PM,  <smiley@zenzebra.mv.com> wrote:
> "Steve Simon" <steve@quintile.net> writes:
>
>> is this native plan9, p9p, or 9vx?
>
> I'm running the stock 386 distribution, on a real hard drive on real
> hardware.  I figured learning a new OS would be simpler without having
> to think about what's virtual versus what's real, versus what's Linux.
>
>> do you definitely have fossil and venti running?
>
> I have no idea.  I just chose the default installation options,
> installing from the CD following the install instructions.  As far as I
> know, "Venti" is a volcano in Italy.
>

In that case, you'll only have Fossil installed.

>> a missing archive/main looks like you don't
>> have archival dumps enabled in fossil.conf?
>
> Oops, s|archive/main|main/archive|
>
>> perhaps you have snapshots enabled?
>
> I know I have "fossil".  I didn't know "dump" and "snapshots" were two
> different things.  Are there any docs that describe these file systems
> in language a newbie has a snowball's chance in Inferno of
> understanding?  The man pages for Plan 9 file systems all seem rather
> opaque... i.e., "cached-worm file system"?
>

Fossil is the "front-end" filesystem. You can run it alone. It can be
configured to take snapshots at regular intervals (I like every 15
minutes, check the fossilcons man page for how to set it up) which
eventually (typically after a few days) expire and are cleared. Venti
is the archival storage; if Venti is present, Fossil will try to make
an archival dump to Venti every morning. The dump is basically a
snapshot, except it's permanent. One side effect is that when a dump
happens, data on Fossil gets replaced with a pointer to a block in
Venti, clearing up your Fossil partition. For that reason, I typically
only allocate a few gigabytes to Fossil and all the rest of the disk
to Venti.

The cached-worm filesystem, cwfs, is related to the old filesystem.
The same goes for "fs" (in many cases, for example the man page
fs(4)), "cwfs", "worm", "kfs", or "kenfs". Erik Quanstrom still uses
kenfs, and based on his positive experiences with it some others have
been experimenting with it as well. However, kenfs requires its own
dedicated machine and is a bit tougher to set up.

I've continually meant to write some sort of beginners-level summary
of the system including things like Fossil and Venti, but the
magnitude of the task is daunting. I may try to do a more clear
description of how the filesystems work together in the near future.

>> what happens if you run 9fs snap?
>
> The mount succeeds, but /n/snap is empty.
>

I don't remember for sure, but it's possible that Fossil doesn't get
configured to take snapshots when Venti isn't installed, for space
reasons. If you can run "fossil/conf /dev/sdC0/fossil" and post the
results here, we'll be able to tell, or you can run the command and
examine the results for yourself based on the fossilcons man page.

If you haven't spent too much time configuring your system, or put too
much on it that cannot be backed up, and if you have a large enough
disk (20 GB should be plenty unless you're storing large files or
music/video), you might want to try re-installing and choosing the
fossil+venti option. This will give you the archival dump storage,
which can be really nice.

John