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Jazz File Systems

This document discusses the different filesystems available on Jazz from the perspective of a Jazz user. You will find that there are three different types of filesystems available on Jazz. Each type has its benefits and drawbacks. Choosing the right location for your files, programs, etc. can have a serious impact on performance and the amount of difficulties you will experience.

The following table lists each of the three types, where you will find them mounted, the pros and cons of each and a discussion about how you might choose to use them.
Type Locations
 Pros Cons Notes
GFS/NFS /home/<username>
Global Namespace
TB filesystem
Large file support(>2GB)
Backed up
Raid protection
Stable hardware
Cache difficulties (NFS)
 Your home directory is located on a GFS filesystem that is NFS mounted. This filesystem is located on a raid array and is served by many different fileservers. This is supposed to provide both a performance increase and protect against the filesystem being inaccessible. If one server goes down, the other servers can continue to serve the filesystems.

We recommend that you keep all your programs and data in your home directory.

You might experience a time lag between when you change a file on one node and when those changes will appear on another (it can be up to 3 or 4 minutes). This is an NFS problem and can not be fixed. You will need to work around it.

PVFS /pvfs/scratch/<username>
Parallel writes to same file
TB filesystem
Large file support(>2GB)
Performance
Raid protection
No cache issues
Problems with many small files
Problems with executables
No support for symlinks
Not backed up
May be cleaned at any time
Hardware is less stable
 If you will have multiple processes and/or multiple nodes writing to the same file(s), then you must to use PVFS for that file(s).

Attempts to run an executable located on a PVFS fs will most likely result in a BUS Fault.

Local /tmp
/sandbox
Fast access
Large file support(>2GB)
Not mounted across nodes
GB filesystem
Not backed up
May be cleaned at anytime
No raid protection
 If you need a place to put temporary files that don't need to be accessed by other nodes, we recommend that you put them into one of these filesystems.

On the compute nodes, these filesystems are automatically cleaned up at the end of each job.


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