[9fans] simple venti demo:

[ron minnich <rminnich@gmail.com>]

I've been working with people who anticipate that big flash that looks
like ram will be available mid/end of the decade. By big, I mean big
as your disk. By RAM, yep, I mean RAM. Reboot, it's all still there.

Needless to say, this changes things a bit. I also noticed the venti
stats: many of the ventis I've seen don't have more than about 30G
used. 30G? I can get a 1U with 512G for 18K nowadays. 1TB for 36K.

Finally, it's always bothered me that to most people, Plan 9 file
systems are a black box. Plan9ports has a very nice "devnull" venti
that seemed like it could be used for a real system.

I thought it might be fun to have a very simple venti that uses an
mmapped backing store and a common hash library (posix hash, available
everywhere) as a demo and to maybe get people wanting to hack in this
area. So on the long boring flight to Spain, I threw one together.

So, see it here: http://pastebin.com/47aC2XGv

To use, just drop into src/cmd/venti, fix mkfile, mk all

to make an arena, the usual dd from /dev/zero

To run, you can, e.g.:
./o.devram -s 2   -a 'tcp!*!6666' /tmp/arenas
the '2' here means two GB. To grow the arena, tack zeros onto the end,
and restart.

To test, used randtest. Or vac. Or whatever.

I've set -s to 32 and had a 32GB venti. Sync is a no-op; it always
syncs on each write. Performance: well, you try it :-)

Mistakes and bugs and things to be done better? Of course! Lucho
pointed out some to me already. You can find more. Hack away!

And, there's going to be a better version soon. I think. But the more
versions floating around, the better.

have fun.

ron