# Using MIT’s Compute Cluster¶

The MKI cluster (with respect to Caterpillar) at MIT has one login node (antares.mit.edu) which connects to a three primary blocks of slave nodes and one analysis node (bigbang.mit.edu).

## Compute Nodes¶

These nodes are accessed through antares.mit.edu (for farming jobs).

### RegNodes¶

Block 1: * 22 nodes (176 cores) * 8 core [2 Ghz] * 16GB memory * 1 Gbit interconnect

Block 2: * 9 nodes (72 cores) * 8 cores, 2.5 Ghz * 16GB memory * 1 Gbit interconnect

This partition should be used for serial jobs. All nodes can be accessed via using the partition RegNodes.

### HyperNodes¶

• 12 nodes (144 cores)
• 12 cores, 2.3 Ghz (24 with hyper-threading)
• 24GB memory
• 10 Gbit interconnect

This partition should only be used for MPI enabled codes as it has faster interconnect.

### AMD64¶

• 8 nodes, 512 cores
• 64 cores, 2.2 Ghz
• 256GB memory
• 10 Gbit interconnect

This partition should only be used for extremely expensive runs which require 100GB++ memory and for codes that are MPI enabled. You can also used openMP multi-threaded jobs which require large amounts of memory (1 job per node). At this stage, there are no time-limits or fixed memory limits for each of the nodes.

## Analysis Nodes¶

The two analysis nodes are Bigbang and Blender.

The Frebel group as MIT also has access to an analysis node which is connected to the Caterpillar data called bigbang. It can be accessed via ssh username@bigbang.mit.edu. See Data Access on this site to get started with your analysis once you understand the storage layout below.

### Storage File Systems/Servers¶

The Frebel group has access to ~120GB RAID storage and 300TB+ of ZFS tape storage. The ZFS tape storage consists of two 130TB servers (grinder and cruncher). These are significantly slower to do I/O from the first time. They each have solid state drives on them acting as a large cache which makes reading data comparable to the RAID drives if you are repeatedly accessing the same snapshot on the tape, for example. The directory structure is as follows:

login node: ssh username@bigbang.mit.edu

# ZFS TAPE STORAGE SERVERS (not as fast as the RAID  slow to load)
-> cruncher/
-> caterpillar/
-> parent/
-> halos/
-> H1079897/

-> grinder/  # ZFS tape drive with
-> caterpillar/
-> halos/
-> H1387186
...
-> aquarius/
-> Aq-A/
-> Aq-B/
-> Aq-C/
-> Aq-D/
-> Aq-E/
-> Aq-F/

# RAID STORAGE
-> data/AnnaGroup/     # RAID drive with all runs lower than LX14
-> caterpillar/
-> halos/            # master folder with all of the caterpillar data within
-> H1079897/        # halos are named according to their folders
...
-> ics/
-> lagr/            # lagrangian volume files
-> parent/           # parent simulation runs
-> gL100X10/        # actual parent simulation (X10 refers to Level_max=10 in MUSIC)


## Current Storage Options¶

We are quite limited with storage space and so we ask you to request more storage if you need it. You will then be allocated a directory on bigbang/data/{username}/. The current break down of the storage capability is as follows:

bigbang% df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/mapper/vg_bigbang-lv_home
57G  1.9G   52G   4% /home
/dev/mapper/vg_bigdata-lv_bigdata
121T   93T   28T  78% /bigbang/data
/cruncher/data
127T  114T   14T  90% /cruncher/data
/grinder/data
127T   74T   54T  59% /grinder/data
/spacebase/data
36T   33M   36T   1% /spacebase/data


## Where is the data actually stored?¶

Due to our storage limitations we have opted for the following strategy

• you should only ever get your hpaths from haloutils via hpaths = haloutils.get_paper_paths_lx(14), for example. Do not get your halo paths from ever going into caterpillar/halos/middle_mass_halos/*.
• all simulation runs lower than LX14 (i.e. LX11,12,13) have been stored on the RAID drives.
• all LX14 runs are symbolically linked on the RAID drives but might not actually exist physically on the drives.
• all halo catalogues are on the RAID drives so access for these is very fast
• all particle data except the last snapshot are actually stored on the ZFS tape drives (though it will appear in outputs/ as a symlink)
• only the last snapshot of the particle data is actually stored on the RAID drives
• all postprocessed catalogues in analysis/ of each halo directory are on the RAID drives
• all of the aquarius data is on the ZFS tape storage as this is not often used
• the parent simulation (gL100X10) is stored in the same way as the LX14 runs: only the last snapshot of the particle data is stored on the RAID drives, everything else is on the ZFS tape drives.

# Submitting Jobs¶

## Example SLURM Submission Scripts¶

Scripts can be submitted via using the command sbatch sub.script. There are a number of options you can specify but the key ones are listed here.

• #SBATCH -n 1 This line sets the number of cores that you’re requesting. Make sure that your tool can use multiple cores before requesting more than one.
• #SBATCH -t 5 This line specifies the running time for the job in minutes. If your job runs longer than the value you specify here, it will be cancelled. There is currently no time limit to jobs so you can leave this out for now.
• #SBATCH -p RegNodes This line specifies the SLURM partition (AKA queue) under which the script will be run. The RegNodes partition is good for routine jobs that can handle being occasionally stopped and restarted. PENDING times are typically short for this queue as it has the most number of cores.
• #SBATCH -o hostname.out This line specifies the file to which standard out will be appended. If a relative file name is used, it will be relative to your current working directory.
• #SBATCH -e hostname.err This line specifies the file to which standard error will be appended. SLURM submission and processing errors will also appear in the file.
• #SBATCH --mail-user=ajk@123.com The email address to which the –mail-type messages will be sent.
• #SBATCH --mail-type=END Because jobs are processed in the “background” and can take some time to run, it is useful send an email message when the job has finished (–mail-type=END). Email can also be sent for other processing stages (START, FAIL) or at all of the times (ALL)

Here a few example scripts. Contact [mailto:brendan.f.griffen@gmail.com Brendan Griffen] if you would like help constructing something more specific. [https://rc.fas.harvard.edu/resources/running-jobs/ Harvard FAS] has a great number of examples and useful tips.

• I have a simple serial job which doesn’t require much memory.
#!/bin/bash
#SBATCH -n 1
#SBATCH -o jobname.o%j
#SBATCH -e jobname.e%j
#SBATCH -p RegNodes
#SBATCH -J jobname
#SBATCH --share

./job.exe

• I have an openMP task which requires a large amount of memory (up to 256GB).
#!/bin/bash
#SBATCH -N 1 -n 64
#SBATCH -o jobname.o%j
#SBATCH -e jobname.e%j
#SBATCH -p AMD64
#SBATCH -J jobname

./job.exe

• I have a MPI job which doesn’t use much memory.
#!/bin/bash
#SBATCH -N 2 -n 16
#SBATCH -o jobname.o%j
#SBATCH -e jobname.e%j
#SBATCH -p RegNodes
#SBATCH -J jobname

mpirun -np 16 ./P-Gadget3 param.txt 1>OUTPUT 2>ERROR

• I have a job which is requires lots of IO between MPI tasks but doesn’t consume much memory.
#!/bin/bash
#SBATCH -n 16
#SBATCH -o jobname.o%j
#SBATCH -e jobname.e%j
#SBATCH -p HyperNodes
#SBATCH -J jobname

mpirun -np 16 ./job.exe

• I have a MPI job which requires a very large amount of memory.
#!/bin/bash
#SBATCH -n 128
#SBATCH -o jobname.o%j
#SBATCH -e jobname.e%j
#SBATCH -p RegNodes
#SBATCH -J jobname

mpirun -np 128 ./job.exe


## Visualizing Cluster Usage¶

The cluster now can be visualized interactively. Just type > sview in the command prompt on antares.mit.edu and you’ll see the an infographic.

Alternatively, you can use Ganglia which can be found here: http://antares.mit.edu/ganglia/

## SLURM Status & Error Help¶

### Status Messages¶

When you type squeue -u username you should see a shortened version of one of the following (e.g. PD for PENDING). You can also see these in the sview.

• PENDING Job is awaiting a slot suitable for the requested resources. Jobs with high resource demands may spend significant time PENDING.

• RUNNING Job is running.

• COMPLETED
Job has finished and the command(s) have returned successfully (i.e. exit code 0).
• CANCELLED
Job has been terminated by the user or administrator using scancel.
• FAILED
Job finished with an exit code other than 0.

### Error Messages¶

• JOB <jobid> CANCELLED AT <time> DUE TO TIME LIMIT
You did not specify enough time in your batch submission script. The -t option sets time in minutes, or can also take hours:minutes:seconds form (12:30:00 for 12.5 hours)
• Job <jobid> exceeded <mem> memory limit, being killed
Your job is attempting to use more memory than you’ve requested for it. Either increase the amount of memory requested by --mem or --mem-per-cpu or, if possible, reduce the amount your application is trying to use. For example, many Java programs set heap space using the -Xmx JVM option. This could potentially be reduced.
• slurm_receive_msg: Socket timed out on send/recv operation
This message indicates a failure of the SLURM controller. Though there are many possible explanations, it is generally due to an overwhelming number of jobs being submitted, or, occasionally, finishing simultaneously. If you want to figure out if SLURM is working use the sdiag command. sdiag should respond quickly in these situations and give you an idea as to what the scheduler is up to.
• JOB <jobid> CANCELLED AT <time> DUE TO NODE FAILURE This message may arise for a variety of reasons, but it indicates that the host on which your job was running can no longer be contacted by SLURM.

Again, see the Harvard FAS SLURM website for extra information and help.