Coda File System

Re: Maximum volume size (was: Some questions...)

From: Phil Nelson <>
Date: Tue, 24 Sep 2002 15:38:32 -0700 (PDT)
Hi Derek,

>	First, can you substantiate your claim about the 1 Gig RVM limit?

It depends on the model your system uses.  Most systems with a 32 bit
address space have a 4G VM limit.  In some cases, the OS takes 2G for
the OS.  Other OSes take less.  You then need space for code, stack
and any shared libs.  Shared libs get memory mapped.  With all this
happening, finding a larger than 1G hole in your VM is hard.  It is
doable, but not on every OS supported by Coda.

>	25 Gig is then the maximum CODA volume size, due to this 1 Gig RVM
>metadata size limit.  Can anyone substantiate this hypothesis?

I have a 40G disk I split as a 25G and a 15G.  Again, the size of RVM
limits the metadata size, not the file space.  If you had an average
file size of 1M, your 1G RVM could serve up a lot more than 25G
of space.  

I have not filled up the RVM with metadata on my 1G RVM servers.

>	Furthermore, does all of the RVM metadata reside in memory at one

With the 1G RVM we recomment using the "mapprivate" feature.  This allows
the OS to use the original file as the place where your RVM file is stored
until you change data.  Only the changes will then chew up your actual
VM space.  It is still a good idea to have enough VM space for the
Coda server and your other servers.  In any case, not all of your 1G RVM
will be in real memory at the same.  I would suspect it would be much
smaller.  On my NetBSD system, the server using 1G RVM (25G files)
shows the following:

root   644  0.0 11.9 5768 15524 ??  S<s  17Sep02     0:11.34 codasrv -n 1
                     ^    ^- Virtual memory size in k bytes
                     |--- Memory resident size of the VM.  

I hope this clarifies things.  

Phil Nelson                       NetBSD:
e-mail:           Coda: 
Received on 2002-09-24 18:39:56