[OpenAFS] Questions, vol. 2.

Hartmut Reuter reuter@rzg.mpg.de
Wed, 21 Jan 2004 19:19:38 +0100

Stephen Bosch wrote:
> More questions!
> -Volumes and volume sizes -- what do you use as a typical volume 
> size/quota? The default is 5 Mb, which is ridiculously small (and points 
> toward an assumption that AFS will be used largely for user home 
> directories). What is too big? For example, I have just created a volume 
> with a 4 Gb quota, as that will comfortably fit on a DVD-R.

We have many home-directory volumes with ~ 5 GB, but the larger a volume 
is the longer takes it
to move it to another server or partition.

> -Volume granularity -- at a minimum, a volume must correspond to one 
> directory, correct? In other words, I can't concatenate volumes invisibly.


> -Another partition question -- on a /vicepxx partition, where does the 
> data actually reside?

If you have a namei-fileserver (under Linux always) they are under 
there is a tree of subdirectories where data belonging to a volume are 
in a common subtree.

> -Unix/AFS user account synchronization: We have two existing 
> workstations that are heavily used. These workstations will also use 
> AFS, but we don't want to move their local home directories to the AFS 
> cell. Do we have to? All the docs seemed geared to that, but all we want 
> is an AFS cell where we can save critical data and then replicate it or 
> back it up.

You don't have to synchronize uids and AFS-ids. It's only nicer to see 
the file ownership correctly
because it is translated by /etc/passwd.

> The docs leave me with the understanding that a client workstation will 
> treat the mounted AFS filespace the same as a mounted local disk. That 
> is, a file owned by user ID 501 in AFS will appear the same as a file on 
>  a local disk owned by user ID 501.
> If I want to create a new user in the cell, does this mean that I have to
> first create a user in AFS
> create a user on the user's workstation with the same UID/GID as the new 
> AFS user?

If you use uss to create the user that may be true. But if you create 
the ptserver entry by hand
you can give the afs user his unix uid by specifying

pts createuser <name> -id <uid>

> -Group IDs -- AFS uses negative group ID numbers. The Linux machines 
> have no idea what to do with that -- they just read the group ID's as "0"
> -afs-modified login, etc. The documentation recommends using the afs 
> modified login. In our case, that essentially means using pam for afs 
> authentication, but as one poster has just pointed out, some 
> applications like openssh don't always function properly with the afs 
> pam module. What do you use in your installations? Is it better to just 
> put klog in the login script?

We use pam and also a "special" slogin which transfers tokens from one 
machine to another.


> Thanks,
> -Stephen-
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Hartmut Reuter                           e-mail reuter@rzg.mpg.de
					   phone +49-89-3299-1328
RZG (Rechenzentrum Garching)               fax   +49-89-3299-1301
Computing Center of the Max-Planck-Gesellschaft (MPG) and the
Institut fuer Plasmaphysik (IPP)