[9fans] Venti config for booting from fs(3)

[9fans] Venti config for booting from fs(3)

[Anthony Sorace]

I'd like to set up my spiffy new cpu server to boot from a venti  
using at least mirrored arenas via fs(3). A few questions on this:
	• I'm mirroring the arenas to insure against drive failure. Does it  
make sense to also interleave the indexes? Both of them?
	• I've got three disks. The venti arenas will be on two. Will the  
indexes benefit significantly from either being interleaved across  
three, or only on the third (with the fossil)? I understand that this  
is somewhat usage-dependent; I guess the real question is how  
sensitive are the indexes to write times?
	• The venti would be used for the fossil boot partition, so needs to  
be there at startup. fs(3) suggests sticking the config on a floppy  
(!). This seems like not the most reliable option. Where are others  
sticking their fs(3) configs for boot?
	• Once there's an fsconfig var, how does the rest of the startup go?  
I don't see it pulling that in anywhere. This needs to be well before  
cpurc, right? Will this require a custom boot?
Anthony

Re: [9fans] Venti config for booting from fs(3)

[erik quanstrom]

since modern disks can read a whole track at once, there's no "reload"
time.  it would only make sense to interleave you have more than 1 i/o
process (venti seems to have a few) and you're either running faster
than the disk bandwidth.  the disk bandwidth could be as high as 60MB/s
for sequential reads and as low as 1MB/s for small reads with many seeks.

if most of venti's io is via the read ahead process, i think there would
be very limited benefit by interleaving i/o.  and you would need four
disks.  if you use two disks partitioned in ½, you will insure that every
write will generate a huge seek.

- erik

RE: [9fans] Venti config for booting from fs(3)

[Joshua Wood]

>   • The venti would be used for the fossil boot partition, so needs to
> be there at startup. fs(3) suggests sticking the config on a floppy
> (!). This seems like not the most reliable option. Where are others
> sticking their fs(3) configs for boot?

The wiki page for mirroring under venti and fossil:
	http://plan9.bell-labs.com/wiki/plan9/ 
Mirroring_with_Fossil_and_Venti/index.html
Suggests storing the fs config in an 'fscfg' parition on the local  
(hard) disk, similar to the conf headers for venti or fossil themselves.

>         • Once there's an fsconfig var, how does the rest of the  
> startup go?
> I don't see it pulling that in anywhere. This needs to be well before
> cpurc, right? Will this require a custom boot?

And then one can set 'fsonfig=' in plan9.ini to the partition created  
above to start devfs with it at boot.

The rest of your questions I'm experimenting with myself & am very  
interested in the experience of others and yours; I do know Russ Cox  
has some informative comments about venti and fossil caching (in  
memory) at the end of the venti-rescue paper. The big hint for a  
single-machine fossil+venti, I thought, is that fossil caches venti  
blocks, too.

--
Josh