Data on the VSC clusters can be stored in several locations, depending on the size and usage of these data. Following locations are available:
- Home directory
- Location available as $VSC_HOME
- The data stored here should be relatively small, and not generating very intense I/O during jobs.
Its main purpose is to stora all kinds of configuration files are stored, e.g., ssh-keys, .bashrc, or Matlab, and Eclipse configuration, ...
- Performance is tuned for the intended load: reading configuration files etc.
- Readable and writable on all VSC sites.
- As best practice, the permissions on your home directory should be only for yourself, i.e., 700. To share data with others, use the data directory.
- Data directory
- Location available as $VSC_DATA
- A bigger 'workspace', for program code, datasets or results that must be stored for a longer period of time.
- There is no performance guarantee; depending on the cluster, performance may not be very high.
- Readable and writable on all VSC sites.
- Scratch directories
- Several types exist, available in $VSC_SCRATCH_XXX variables
- For temporary or transient data; there is typically no backup for these filesystems, and 'old' data may be removed automatically.
- Currently, $VSC_SCRATCH_NODE, $VSC_SCRATCH_SITE and $VSC_SCRATCH_GLOBAL are defined, for space that is available per node, per site, or globally on all nodes of the VSC (currently, there is no real 'global' scratch filesystem yet).
- These file systems are not exported to other VSC sites.
Since these directories are not necessarily mounted on the same locations over all sites, you should always (try to) use the environment variables that have been created.
Quota is enabled on the three directories, which means the amount of data you can store here is limited by the operating system, and not just by the capacity of the disk system, to prevent that the disk system fills up accidentally. You can see your current usage and the current limits with the appropriate quota command as explained on the page on managing disk space. The actual disk capacity, shared by all users, can be found on the Available hardware page.
You will only receive a warning when you reach the soft limit of either quota. You will only start losing data when you reach the hard limit. Data loss occurs when you try to save new files: this will not work because you have no space left, and thus you will lose these new files. You will however not be warned when data loss occurs, so keep an eye open for the general quota warnings! The same holds for running jobs that need to write files: when you reach your hard quota, jobs will crash.
This directory is where you arrive by default when you login to the cluster. Your shell refers to it as "~" (tilde), or via the environment variable $VSC_HOME.
The data stored here should be relatively small (e.g., no files or directories larger than a gigabyte, although this is not imposed automatically), and usually used frequently. The typical use is storing configuration files, e.g., by Matlab, Eclipse, ...
The operating system also creates a few files and folders here to manage your account. Examples are:
|.ssh/||This directory contains some files necessary for you to login to the cluster and to submit jobs on the cluster. Do not remove them, and do not alter anything if you don't know what you're doing!|
|This script defines some general settings about your sessions,|
|.bashrc||This script is executed every time you start a session on the cluster: when you login to the cluster and when a job starts. You could edit this file to define variables and aliases. However, note that loading modules is strongly discouraged.|
|.bash_history||This file contains the commands you typed at your shell prompt, in case you need them again.|
In this directory you can store all other data that you need for longer terms. The environment variable pointing to it is $VSC_DATA. There are no guarantees about the speed you'll achieve on this volume. I/O-intensive programs should not run directly from this volume (and if you're not sure, whether your program is I/O-intensive, don't run from this volume).
This directory is also a good location to share subdirectories with other users working on the same research projects.
To enable quick writing from your job, a few extra file systems are available on the work nodes. These extra file systems are called scratch folders, and can be used for storage of temporary and/or transient data (temporary results, anything you just need during your job, or your batch of jobs).
You should remove any data from these systems after your processing them has finished. There are no guarantees about the time your data will be stored on this system, and we plan to clean these automatically on a regular base. The maximum allowed age of files on these scratch file systems depends on the type of scratch, and can be anywhere between a day and a few weeks. We don't guarantee that these policies remain forever, and may change them if this seems necessary for the healthy operation of the cluster.
Each type of scratch has his own use:
- Shared scratch ($VSC_SCRATCH)
To allow a job running on multiple nodes (or multiple jobs running on separate nodes) to share data as files, every node of the cluster (including the login nodes) has access to this shared scratch directory. Just like the home and data directories, every user has its own scratch directory. Because this scratch is also available from the login nodes, you could manually copy results to your data directory after your job has ended. Different clusters on the same site may or may not share the scratch space pointed to by $VSC_SCRATCH.
This scratch space is provided by a central file server that contains tens or hundreds of disks. Even though it is shared, it is usually very fast as it is very rare that all nodes would do I/O simultaneously. It also implements a parallel file system that allows a job to do parallel file I/O from multiple processes to the same file simultaneously, e.g., through MPI parallel I/O.
For most jobs, this is the best scratch system to use.
- Site scratch ($VSC_SITE_SCRATCH)
A variant of the previous one, may or may not be the same. On clusters that have access to both a cluster-local scratch and site-wide scratch file system, this variable will point to the site-wide available scratch volume. On other sites it will just point to the same volume as $VSC_SCRATCH.
- Node scratch ($VSC_SCRATCH_NODE)
Every node has its own scratch space, which is completely separated from the other nodes. On many cluster nodes, this space is provided by a local hard drive or SSD. Every job automatically gets its own temporary directory on this node scratch, available through the environment variable $TMPDIR. $TMPDIR is guaranteed to be unique for each job.
Note however that when your job requests multiple cores and these cores happen to be in the same node, this $TMPDIR is shared among the cores! Also, you cannot access this space once your job has ended. And on a supercomputer, a local hard disk may not be faster than a remote file system which often has tens or hundreds of drives working together to provide disk capacity.
- Global scratch ($VSC_SCRATCH_GLOBAL)
We may or may not implement a VSC-wide scratch volume in the future, and the environment variable VSC_SCRATCH_GLOBAL is reserved to point to that scratch volume. Currently is just points to the same volume as $VSC_SCRATCH or $VSC_SITE_SCRATCH.