Any way to "passive commit" to RAM without syncing ?

[Swift Griggs <swiftgriggs%gmail.com@localhost>]

I know NetBSD supports RAM disks. I also know it uses them for 
installation, but I'm not sure if they are overlays on top of the static 
disk images or if they get loaded/populated with the image after the 
system boots. The effect is the same, either way. You end up with a 
writable file system in RAM which is predicated on a disk image. I was 
thinking about this in the context of another problem.

Let's say I've got a machine with a boatload of RAM and I have an 
application which wants extremely fast writes, but doesn't really care 
that much about data integrity, and this case, nor do I. Having the system 
come back in the same state after rebooting is "nice to have" in this 
thought experiment. Soo, here is the question:

Since a RAM disk is probably the fastest option, is there a way to 
basically leave uncommitted data until I run "sync" or something calls 
fsync() ? Even better, is there a way to fake a sync until I run something 
else ?

In other words, operate out of a RAM disk until my human operator gives 
the go-ahead to flush out the writes to disk or the RAM disk gets full. I 
think Sprite did something like this back in the Jurassic Period. I also 
remember CacheFS for Solaris doing something similar for NFS.

I can think of a few applications:

- Internet cafe style browsing where the machines are using older 
hardware. They might benefit from using a small RAM disk overlay rather 
than having to use something like a PATA disks for it's cache.

- Editing high bandwidth data like video or audio. Most of the time my 
editing sessions don't last more than an hour and once I get a final cut I 
just save the project to a server and don't care much about the recording 
or editing workstation.

- Any kind of temporary storage that needs RAM disk speeds, but still 
needs an option to sync/flush the file system back to long term storage.

I'm guessing this would be a little tricky with something like UFS since a 
process could alter/write to a file and it'd need to reflect that when 
another process wanted to do the same, fseek(), or dozens of other 
operations. However, I just wonder if there is already a way to do this 
and I'm just not aware of it.

I wonder if the LiveCD's for Linux that let you flush you changes to USB 
do something similar. I doubt it. I'm guessing they just load a RAM disk 
image and you operate on that until you reboot and it's lost.

-Swift