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Login

• You have to be member of HPC_user (can be applied for on id.awi.de, Start a new request > IT Services > select High-Performance-Computing (HPC) > Add to cart). See HPC account for more info.
• The login nodes can be accessed via
  ssh albedo0.dmawi.de and ssh albedo1.dmawi.de
  → If you do not familiar with ssh and/or bash you should start here for a basic introduction.
• Please do not use these login nodes for computing, please use the compute nodes (and take a look at our hardware and slurm documentation)
• HPC resources are not available from remote for security reasons (VPN is possible).
• By using albedo you accept our HPC data policy
• You can ssh to-a-node where a job of yours is running, if (and only if) you have a valid ssh-key pair. (e.g. on a login node: ssh-keygen -t ed25519;  ssh-copy-id albedo1)
  Make sure your key is secured with a password!

Software

• Albedo is running the operating system Rocky Linux release 8.6 (Green Obsidian).
• Slurm 22.05 is used as the job scheduling system. Important details on its configuration on Albedo are given here: Slurm.
• Details on the user software can be found here: Software.

Environment modules

On albedo we use environment modules to load/unload specific versions of software. Loading a module modifies environment variables so that the shell e.g. knows where to look for binaries.

You get an overview of all software installed by typing

module avail

To load and unload a module use

# load
module load <module>

# unload
module unload <loaded module>

Sometimes it might be useful to unload all loaded modules at once. This is done with

module purge

It is also possible to use the module command from some scripting languages. For example, in Python you can do:

$ python
Python 3.8.16 | packaged by conda-forge | (default, Feb  1 2023, 16:01:55)
[GCC 11.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> module_python_init = "/usr/share/Modules/init/python.py"
>>> exec(open(module_python_init).read())
>>> result = module("list")
Currently Loaded Modulefiles:
 1) git/2.35.2   2) conda/22.9.0-2
>>> result is True
True

Usage of a node's internal NVMe storage

All compute (including fat and gpu) nodes have a local NVMe disk mounted as /tmp. The GPU nodes have an additional storage /scratch. See System overview for the exact sizes.  We strongly encourage you to use these node-internal storage, which is faster than the global /albedo storage, if your job does lots of reading/writing. In particular, it might be beneficial to write your job output to the local disk and copy it to /albedo after your job is finished.

# Copy input data to the node, where your main MPI (rank 0) task runs
rsync -ur $INPUT_DATA /tmp/

# If you need the input data on every node, you have to add `srun` in front of the copy command
srun --ntasks-per-node=1 rsync -ur $INPUT_DATA /tmp/

# do the main calculation
srun $MY_GREAT_PROGRAM

# Copy your results from node where main MPI (rank 0) task runs to global storage
# If data is written on all nodes, start rsync using srun, as above
rsync -r /tmp/output/* /albedo/scratch/$MYPROJECT/output/

CPU, Memory, and Process Time Restrictions on a Login Node

On the login nodes albedo0 and albedo1, you have limits for what a process is allowed to do. Note please that the login nodes are not available for computing, and should be used for simple shell usage only! You get a total of 2048 processes (PIDs), 9 logins

Have a look at /etc/security/limits.conf. For further details.

Monitoring

Files

• info.sh -f <file> shows if a file is on NVMe or HDD

Node usage monitoring

• Try info.sh -l to get output of cat /proc/loadavg and vmstat -t -a -w -S M of all nodes your jobs are running. Use info.sh -L  to add output of top -b -n1 -u$USER
• ssh prod-xyz where a job of yours is running and try something like [h]top or vmstat -t -a -w -S M 1
  
• info.sh -S to see running jobs and resources used from finished slurm jobs.
  

GPU monitoring

When using the GPUs you can monitor their usage with