When you are writing large files to /scratch or /group, it is recommended to stripe these across multiple partitions (Lustre OSTs). When you have very large files (>1TB), you must stripe them as they can rapidly fill the OST and cause I/O issues for you and other users.
By default, files on /scratch and /group are not striped, so when a large file is written to a single OST, it can limit your I/O performance. You will need to set the file striping (or file layout) before writing the file, or migrate the file if it has already been written.
Step-by-step guide - creating and setting a new striped directory
For creating a new directory and setting the file layout for new files. This will only affect newly written files, see migration below to apply striping to already existing files.
Create a directory which will contain your files:
Designate the directory for striping and the number of OSTs to stripe it over, 4 in this example:
Newly written files in this directory will be striped over the specified number of partitions. This can be confirmed:
Step-by-step guide - striping an existing file through migration
For retroactively setting the file layout on existing files. Migration will copy the file in place and spread it across the specified number of OSTs.
Check the current layout on the existing file(s) to confirm they do not have the desired file layout:
Migrate the existing file(s) with the desired file layout:
Confirm that your changes have been set