Filestores¶

/home directory¶

All users have a home directory in the location /home/yourusername.

ShARC and Iceberg share the same /home directory. and is accessible to all worker and login nodes.

Bessemer has a separate /home directory``, which is accessible to all worker and login nodes on Bessemer.

Backup policy: /home has backup snapshots taken every 4 hours and we keep the 10 most recent. /home also has daily snapshots taken each night, and we keep 28 days worth, mirrored onto a separate storage system.

The filesystem is NFS.

/data directory (Iceberg and ShARC only)¶

Every user on Iceberg and ShARC has access to a much larger data-storage area provided at the location /data/yourusername.

The quota for this area is 100 GB per user.

This area is shared between ShARC and Iceberg and is accessible to all worker and login nodes.

Backup policy: /data has snapshots taken every 4 hours and we keep the 10 most recent. /data also has daily snapshots taken each night, and we keep 7 days worth, but this is not mirrored.

The filesystem is NFS.

Note: the directory /data/yourusername is made available to you (mounted) on demand: if you list the contents of /data after first logging on then this subdirectory might not be shown. However, if you list the contents of /data/yourusername itself or change into that directory then its contents will appear. Later on if you list the contents of /data again you may find that /data/yourusername has disappeared again, as it is automatically unmounted following a period of inactivity.

/fastdata directory¶

Users on ShARC and Bessemer can access a large fast-access data storage area under /fastdata.

You can access ShARC’s /fastdasta storage on Iceberg, under the directory path /fastdata-sharc.

ShARC’s /fastdata area provides 669 TeraBytes of storage. Bessemer’s /fastdata area provides 460 TeraBytes of storage.

In order to avoid interference from other users’ files it is vitally important that you store your files in a directory created and named the same as your username. e.g.

mkdir /fastdata/yourusername

By default the directory you create will have world-read access. If you want to restrict read access to just your account then run

chmod 700 /fastdata/yourusername

after creating the directory. A more sophisticated sharing scheme would have private and public directories

mkdir /fastdata/yourusername
mkdir /fastdata/yourusername/public
mkdir /fastdata/yourusername/private

chmod 755 /fastdata/yourusername
chmod 755 /fastdata/yourusername/public
chmod 700 /fastdata/yourusername/private

ShARC nodes access /fastdata using the high-performance Onnipath network interconnect. Access to Bessemer’s /fastdata storage is via 25GbE ethernet networking. Iceberg nodes access ShARC’s /fastdata storage using 1GbE ethernet network.

/fastdata is optimised for large file operations. it is faster than /home/, /data and /shared (see below) when dealing with larger files but does not handle lots of small files very well: it is less efficient than /scratch (see below) when dealing with smaller files. An example of how slow it can be for large numbers of small files is detailed at http://www.walkingrandomly.com/?p=6167

You can use the lfs command to find out which files under /fastdata are older than a certain number of days and hence approaching the time of deletion. For example, to find files 50 or more days old

lfs find -ctime +50 /fastdata/yourusername

Backup policy: /fastdata is not backed up.

/fastdata uses the Lustre filesystem. This does not support POSIX locking which can cause issues for some applications (e.g. programs that create/use SQLite databases).

/shared directories¶

IT Services now provide 10 terabytes of shared storage for free per research group. After the storage has been requested/purchased by a group’s PI and then provisioned by IT Services it can be accessed by name

• as a Windows-style (SMB) file share on machines other than ShARC/Iceberg using \\uosfstore.shef.ac.uk\shared\;
• as a subdirectory of /shared on ShARC/Iceberg (you need to explicitly request HPC access when you order storage from IT Services).

Note that this subdirectory will be mounted on demand on ShARC/Iceberg: it will not be visible if you simply list the contents of the /shared directory but will be accessible if you cd (change directory) into it e.g. cd /shared/my_group_file_share1

If you need to access a /shared area on Bessemer please contact helpdesk@sheffield.ac.uk to arrange this.

Regarding permissions: behind the scenes, the file server that provides this shared storage manages permissions using Windows-style ACLs (which can be set by area owners via the Research Storage management web interface. However, the filesystem is mounted on a Linux cluster using NFSv4 so the file server therefore requires a means for mapping Windows-style permissions to Linux ones. An effect of this is that the Linux mode bits as seen on ShARC/Iceberg are not always to be believed for files under /shared: the output of ls -l somefile.sh may indicate that a file is readable/writable/executable when the ACLs are what really determine access permissions. Most applications have robust ways of checking for properties such as executability but some applications can cause problems when accessing files/directories on /shared by naievely checking permissions just using Linux mode bits:

• which: a directory under /shared may be on your path and you may be able to run a contained executable without prefixing it with a absolute/relative directory but which may fail to find that executable.
• Perl: scripts that check for executability of files on /shared using -x may fail unless Perl is explicitly told to test for file permissions in a more thorough way (see the mention of use filetest 'access' here).
• git: may complain that permissions have changed if a repository is simply moved to /shared/someplace from elsewhere on ShARC/Iceberg. As a workaround you can tell git to not to track Linux permissions for a single repository using git config core.filemode false or for all repositories using git config --global core.filemode false.

The documentation for the /shared storage serivce includes information on:

• how access/permissions are managed
• how to create folders with associated permissions within /shared storage areas

/scratch: for reading/writing small files¶

For jobs that need to read/write lots of small files the most performant storage will be the temporary storage on each node (under the /scratch directory).

This is because with /home, /data, /fastdata and /shared each time a file is accessed the filesystem needs to request ownership/permissions information from another server and for small files these overheads are proportionally high. However, for /scratch such ownership/permissions metadata is available on the local machine, so it is faster when dealing with small files.

The most obvious disadvantage to the /scratch node-local storage is that a given directory cannot relabily be accessed between jobs as you cannot guarantee that your next job will run on the same node. Any data of value must therefore be copied off /scratch (e.g. to /home or /data) before the end of your job.

Where to store data within ``/scratch``: The scheduler automatically creates a per-job directory for you under /scratch. If you started your job using qrshx, qsh or qsub then the name of this directory is stored in the $TMPDIR environment variable e.g.

[[email protected] ~]$ qrshx
[[email protected] ~]$ cd $TMPDIR
[[email protected] 667443.1.all.q]$ pwd
/scratch/667443.1.all.q

The scheduler will then clean up (delete) $TMPDIR at the end of your job, ensuring that the space can be used by other users.

If using qrsh to start your job then the environment variable will unfortunately be undefined so you will need to manually create a directory under /scratch (named using your username) and this will not be cleaned up when the job ends.

Anything under the /scratch may be deleted periodically when the worker-node is idle. /scratch is not backed up. There are no quotas for /scratch storage.

/scratch uses the ext4 filesystem.

Determining your current filestore allocation¶

To find out your current storage quota usage for /home and /data:

quota

If you exceed your file storage allocation¶

As soon as the quota is exceeded your account becomes frozen. In order to avoid this situation it is strongly recommended that you:

• Use the quota command to check your usage regularly.
• Copy files that do not need to be backed up to the /fastdata/username area, or remove them from ShARC/Iceberg completely.

Recovering snapshots¶

We take regular back-ups of your /home and /data directories and it is possible to directly access a limited subset of them.

There are 7 days worth of snapshots available in your /home and /data directories in a hidden directory called .snapshot. You need to explicitly cd into this directory to get at the files:

cd /home/YOURUSERNAME/.snapshot

The files are read-only. This allows you to attempt recover any files you might have accidentally deleted recently.

This does not apply for /fastdata for which we take no back-ups.