Using Filestore on the HEC

Overview of filestore

User accounts on the HEC have three high performance personal filestore areas - home, storage and scratch - which are available across the cluster. Each job also has access to a unique temp directory. These areas differ in size, backup policy and file retention policy.

The home area is subject to a small (10G) quota. The home area is backed up nightly for 90 days, and should be used for essential files (e.g. job submission scripts and your own codes).

The storage area has a larger quota (100G) but is not backed up. This area should typically be used to store job outputs, your own applications, or other research data that can be regenerated if lost.

The scratch area is a large (10T) shared area; files written to it are automatically deleted after four weeks. The scratch area is intended as a place to hold very large job output files and other data files for a limited period of time - files will be deleted from scratch four weeks after they were last written to.

Finally, the temp area is a unique directory available to each job. The directory exists on the local disk of the compute node running the job, and is intended to provide fast file I/O for jobs which create temporary files during their run. The contents of temp are automatically deleted at the end of each job, so any essential files created here should be copied into one of the home, storage or scratch areas before the job terminates.

A summary of the different filestores area is given below:

File Area

Quota

Backup Policy

File Retention policy

home

10G

Nightly for 90 days

Permanent

storage

100G

None

Permanent

scratch

10T

None

Files automatically deleted after 4 weeks

temp

Unlimited

None

Files automatically deleted at the end of the job

Home, storage, scratch and temp can be quickly referenced via the environment variables HOME, global_storage, global_scratch and TMPDIR respectively. For example, to quickly change directories to your scratch area, type: cd $global_scratch. The variables can also be used in standard Linux commands within job scripts, though not in #SBATCH lines.

Viewing filestore quota and usage

You can view your home, storage and scratch usage at any time using the command gpfsquota, which presents output from the mmlsquota command in a more readable format. Typical output from gpfsquota looks like this:

Filesystem          Quota      Used     Avail     Use%     # files
home                  10G     5.50G     4.50G    55.00      24840
storage              100G    44.00G    56.00G    44.00      80640
scratch            10240G  2001.00G  8239.00G    19.54         23

For each filestore area the output shows the following info: your quota limit; how much you’ve used; how much is available; a percentage usage; and the total number of files you have in that area.

Best practice using the Filestore

The main HEC filestores are shared across the login node and all compute nodes. With several thousand user jobs accessing the filestore simultaneously, we offer some best practice guidelines to avoid overloading the filesystem. When running many jobs at once, particular care should be taken to follow the guidelines below:

Avoid making multiple jobs write to same the file. Multiple processes or jobs writing to the same file at the same time in an uncoordinated manner will result in missing or corrupted data. It will also slow the filesystem down as the write requests to a single file are queued up to run.

Avoid creating large directories Directories become increasingly slower to manage (e.g. to view, add or delete files) the larger they become. Avoid placing more than a few thousand files in the same directory. Large directories should be deleted after use rather than reused - the directory size on disk never shrinks, even when files within it are deleted, making it slower to use next time.

Avoid excessive file copying within jobs. Copying data from one location on the filesystem to another is an expensive operation - consider ways to minimise it, especially when running hundreds of jobs at the same time. For applications which need a local copy of an input file, consider using the ln -s command to create a soft link (short cut) rather than a full copy of the file. If output files need to be placed elsewhere on the filesystem, consider using the mv (file move) command.

Avoid directory recursion/file searching within jobs. Having multiple jobs search for specific files through a large directory hierarchy can place a high load on the filesystem. Avoid use of recursive commands such as find within jobs.

Use the temp directory for temporary files. The temp directory (referenced by the $TMPDIR variable) is located on the compute node running your job, and offers much higher file I/O and bandwidth and lower latency than network based storage. Wherever possible create any temporary/transient files in temp.

Clean up your filestore regularly. With the ability to run hundreds of jobs simultaneously, user filestore can quickly become cluttered with files (e.g. job stdout and stderr files). Small files in particular have a relatively high space overhead - even a small file will consume 32k of quota due to metadata and RAID overheads. An area filled with large numbers of small files can exhaust quota more quickly than expected.

Offload valuable data to a permanent location. The HEC filestore is intended to enable high performance access to files for job runs, and should not be used for long term archiving of research data. Important research results should be offloaded from the HEC as soon as convenient to a more suitable location, such as LUNA. Please contact your local departmental IT liaison to discuss options for long-term research data archiving.

Transferring files to and from the HEC

Transferring files to the HEC from the IUS or a Linux or Mac desktop

Files may be copied from your local machine (e.g. Linux desktop or the IUS) into your HEC filestore by using the command scp on your desktop/the IUS in the format below:

scp myfilename username@wayland-2022.hec.lancaster.ac.uk:mydirectory

This will copy myfilename in the current directory into the directory mydirectory on the HEC.

Files can also be copied from the HEC onto your local machine by running this command on your local machine:

scp username@wayland-2022.hec.lancaster.ac.uk:myfilename mydirectory

This will copy myfilename from the HEC into mydirectory on your local machine.

The first time you use scp, it may prompt you with the following:

Host key not found from the list of known hosts.
Are you sure you want to continue connecting (yes/no)? yes

Reply with yes and you will then receive a prompt for your password. With subsequent logins you will only have to give your password.

To copy directories and their contents, use scp -r, for example :

scp -r mydirectory username@wayland-2022.hec.lancaster.ac.uk:mydirectory

The scp command defaults to your home directory on the HEC, so relative file paths should start from there. For storage, scratch or other filestore areas using the full directory path is recommended. If you have difficulty determining the full path to a directory a useful approach is to login to the HEC in a separate window, use the cd command to change to the desired directory and then run the command pwd (print working directory) which will show the full path to the directory. This can then be copy-and-pasted into your desktop/IUS window containing the scp command.

Transferring files to the HEC from a Windows PC

Transferring files between the HEC and a local desktop PC requires your PC to run a client application capable of the secure file transfer protocol. There are several applications which support this. One such application is WinSCP, which can be found on AppsAnywhere.

Tip

Take care to ensure that text files such as job scripts are transferred in text mode in order to avoid problems caused by format differences between Unix and Windows text files. Binary files (i.e. files whose contents are not solely ASCII text) should be transferred in binary mode.

Transferring files to the HEC from Luna or other smb-compliant services

The HEC login node has a high bandwidth connection to Luna, the ISS-managed research data archive. While users can transfer files between folders on Luna and the HEC using their PC, for large file transfers using the smbclient tool to connect from the HEC directly to Luna is much faster.

To connect to a folder on Luna, smbclient needs two pieces of information:

Faculty code: Faculty codes are typically the faculty’s acronym (e.g. FST for Faculty of Science and Technology, FASS for Faculty of Applied and Social Sciences) and are viewable from the top level of the \\luna tree under the Windows File Explorer.

The folder path: The path is the series of subfolders required to navigate the tree to the required subdirectory.

The command to connect to a folder on Luna is then:

smbclient -D folder-path //luna/faculty-code

Here’s an example for accessing the py/gondor folder - a restricted-access folder for a research group in the Faculty of Science and Technology:

wayland-2022% smbclient -D py/gondor //luna/fst
Enter LANCS\testuser's password:
Try "help" to get a list of possible commands.
smb: \py\gondor\>

You will be prompted to enter your password to authenticate your acecss to the requested folder. The smb: prompt will then allow you to use ftp-like commands such as put and get to transfer files and cd to navigate between subfolders. You can use the help command from the smb prompt to view a list of possible commands.

Here’s an example of uploading a file to the folder:

smb: \py\gondor\> put myfile

putting file myfile as \py\gondor\myfile (529105.6 kb/s) (average 529105.6 kb/s)

The transfer speed here is notably higher than via file transfer on Windows, as the data is passed directly from the HEC to the folder on Luna without having to pass through the user’s PC first.

Using Kerberos tickets with smbclient

If you are using smbclient several times during a session, you may find it useful to use a kerberos ticket to remove the need to repeatedly enter a password for authentication. Logging in to the HEC will automatically generate a kerberos ticket for you which is valid for 24 hours. To use the kerberos ticket, simply add the -k argument to the smbclient command:

smbclient -k -D folder-path //luna/faculty-code

If your ticket has expired, you can generate a new one by running the kinit command and entering your regular password.

For more advanced usage of smbclient, use the command man smbclient to view the command’s manual page.