File System

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Revision as of 13:58, 27 January 2014 by Toddr (talk | contribs) (Barn (long-term storage))

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CCI is moving to the unified GPFS file system.

General Layout

The Unified CCI GPFS filesystem is built using a block size of 8MiB. Performance testing indicated this was about optimal for our storage system hardware. Applications using large-record I/O will benefit most from the large block size. Performance testing shows that applications with small-record I/O perform at least nearly as well with the large block size as in a file system with a much smaller block size.

The file system is broken into three main areas: home, scratch, and barn. Each area of the filesystem has its own purpose and tradeoffs.




The home area contains user home directories, organized by projects. User home directories are only writable by the user. This area of the filesystem has a 10 GiB quota. Replication is used to help protect data.

Please note: In GPFS, replicated files are counted twice during quota calculations. This means the home directory limit is effectively 5 GiB per project (sum of every project user's home directory usage).

Home directories are intended to store only your "dot files" and maybe a few other configuration files, scripts, or small programs you need to customize your working environment. Program files, data sets, etc. should be stored in your barn.

Users with a legacy home directory will find a link in their new home directory, legacy-home, pointing to the old home directory. You can remove this link once you no longer need your legacy data.

Once the legacy file systems are retired, we plan to migrate home directories to higher-speed storage. This should help interactive sessions to be more responsive even in the face of heavy load.

Scratch (short-term storage)

There is a scratch data directory for each project and its associated users, as well as corresponding links in each user's home directory. This space is meant as a temporary staging area for performing computation. Performance in this directory will be better than in the home or barn areas. This space does not have a quota.

Each home directory contains a link, scratch, to the user's personal scratch space, and a link, scratch-shared, to the project's shared scratch space.

Important: This space will periodically be purged of files older than 14 days. This policy is subject to change based on filesystem demands. If longer-term storage of data is necessary it should be stored in the barn area.

Important: Because scratch space is not replicated, it is vulnerable to data loss or corruption if we suffered a serious storage system failure. We may remove files before their normal expiration date if we suspect there is data corruption. (Data in the home or barn areas are replicated and thus more resilient to failure.)

Barn (long-term storage)

There is a barn directory for each project and its associated users with corresponding links in each user's home directory. This space is meant to allow for longer-term storage of working data and programs than allowed by the scratch area. It is not meant for long-term retention of results, but rather is the space to store the tools you need to do your work. Nor is it intended to be the area where your computations run; they will perform better out of scratch. You may want to keep your actual executables in the barn, stage up data in scratch for several jobs using data sets stored in your barn, and copy back final results to your barn until you can properly retrieve them to your own local long-term storage.

Each project's barn starts with a 10 GiB quota. Like home, it is replicated, and it is never automatically purged of old files. Project users must manage their own space usage in the barn.

Each home directory contains a link, barn, to the user's personal barn space, and a link, barn-shared, to the project's shared barn space.

Additional space may be allocated to a project's barn at the discretion of the CCI Director upon written request by the project PI. Any extended quotas are subject to periodic review and potential reduction at the discretion of the Director.