> We (ir.stanford.edu) are thinking about changing the way we layout
> home directories in AFS and would like to get some feedback on what...
> [using] /afs/ir/users/[a-z]/$USER /afs/ir/users/u/username
> [considering] /afs/ir/users/[a-z]/[a-z]/$USER /afs/ir/users/u/s/username
> [or maybe] /afs/ir/users/NNNN/$USER NNNN random distributed
> Other options I've thought of include hashing on the uid, doing some sort
> of modulo arithmetic on the uid, or treating the uid as a hex number and
> using them to create the subdirectories. The problem with this method is
> if your UID changes then so does your directory name (unless you have some
> huge directory full of symlinks which defeats the whole purpose if you use
> this directory in a password file). These approaches also make it harder
> to find someone's home directory (although ~user works fine if you have
> the full password file on your system).
> We could eventually have about 20,000 directories in AFS/DFS if we migrate
> all our users into AFS.
We are fairly close to 20,000 users in AFS home-directories.
We've gone to:
/afs/isu/users/NN/MM/username
where MM are the 5 LS bits of username's uid and NN are the next LS 5 bits.
(Only in the most dire circumstances would we change a UID, so that's not
an issue with us.) For example:
pooh.cc> hesinfo janeane filsys
AFS /afs/iastate.edu/users/19/27/janeane w /home/janeane
pooh.cc> hesinfo janeane passwd
janeane:*:5755:101:,,,,:/home/janeane:/bin/tcsh
5755 = 101001111011
\ /\ /
\ / \ /
=19 =27
This gives us nice small directories down to the user:
pooh.cc> ls /afs/isu/users
00 02 04 06 08 10 12 14 16 18 20 22 24 26 28 30
01 03 05 07 09 11 13 15 17 19 21 23 25 27 29 31
pooh.cc> ls /afs/isu/users/19
00 02 04 06 08 10 12 14 16 18 20 22 24 26 28 30
01 03 05 07 09 11 13 15 17 19 21 23 25 27 29 31
pooh.cc> ls /afs/isu/users/19/27
atreptow emanuele havoc jilleneh mash ptcullen wwiese
brizious fareway hccheng jsturges mgruber pwilliam ylh
cjnelson grau janeane lfevold narcisus rachelj
We also have a dir of symlinks (/afs/isu/usr/username) but that's
so slow it's hardly used.
He use the hesiod naming service (a minor extention of DNS) and
a program called "attach" (the original MIT version available
from athena-dist.mit.edu I should think) to do the lookup.
Attach does a lot of nifty things, but the major result is a
symlink from /home/username to /afs/isu/users/NN/MM/username
(looked up using hesiod). Invoking attach as "detach" does
the expected thing. Our /bin/login does an "attach username"
for the user.
By attaching/detaching as needed, /home stays fairly small
too:
pooh.cc> ls /home
OSFDOC ftp ispaid milner public userve
compression gcc janeane motd pv-tech www
decathena ghost john news:rdb tex x11r5
emacs gnu jzelle nfs1test tigger xfer
explorer graphics michaelv olc ultrix xfig
Appended below is a run of our attach in debug mode so you
can sort of see what it does.
Hope this is some help,
John
------------------------------------------------------------------------------
config(janeane/axp) = Not Found
hesiod(janeane/axp) = Not Found
config(janeane) = Not Found
hesiod(janeane) = AFS /afs/iastate.edu/users/19/27/janeane w /home/janeane
janeane resolves to:
AFS /afs/iastate.edu/users/19/27/janeane w /home/janeane
Attachtab locked (1)
Freeing attachtab
Retrieving attachtab
Scanning attachtab for janeane entry
Attachtab entry for janeane not found
Setting lock on /tmp/attach_janeane: 6
Storing attachtab
Freeing attachtab
Unlocking attachtab (1)
Processing line: AFS /afs/iastate.edu/users/19/27/janeane w /home/janeane
mode is w, override is (ignored for AFS)
add option(soft) (ignored for AFS)
Making mountpoint for /home/janeane (really a symlink for AFS)
execing /usr/athena/bin/aklog as:
aklog -path /afs/iastate.edu/users/19/27/janeane -zsubs
zsub: iastate.edu:root.cell
Adding zephyr instance iastate.edu:root.cell.
zsub: iastate.edu
Adding zephyr instance iastate.edu.
zsub: iastate.edu:users
Adding zephyr instance iastate.edu:users.
zsub: iastate.edu:user.janeane
Adding zephyr instance iastate.edu:user.janeane.
zsub: fs-5.iastate.edu
Adding zephyr instance fs-5.iastate.edu.
lstating /afs/iastate.edu/users/19/27/janeane
lstating /home/janeane
Mountpoint canonicalized as: /home/janeane
symlinking /afs/iastate.edu/users/19/27/janeane to /home/janeane
janeane: AFS mounted /afs/iastate.edu/users/19/27/janeane on /home/janeane (read-write)
Attachtab locked (1)
Freeing attachtab
Retrieving attachtab
Storing attachtab
Unlocking attachtab (1)
Freeing attachtab
Removing lock on /tmp/attach_janeane
Subscribing to 5 zephyr instances.
------------------------------------------------------------------------------
John Hascall ``An ill-chosen word is the fool's messenger.''
Systems Software Engineer
Project Vincent
Iowa State University Computation Center + Ames, IA 50011 + 515/294-9551
