Quota
Fundamentals
Quotas are used to limit how much space and how many files users and projects can have in each data store. This prevents things like a runaway or buggy job using up the filesystem’s entire capacity rendering it unusable for other users and projects on the cluster, as well as preventing steady accumulation of unused files. Data stores have two different kinds of quotas which may be set:
- Block
- Quota limiting how much space can be used (i.e. how many blocks on the filesystem).
- Note that because filesystems store files in blocks, the usage rounds up to the nearest block in many cases (e.g. a 1 byte file often takes up 4 KiB of space).
- Inode
- Quota limiting how many files, directories, and links can be used.
- In most filesystems, every file, directory, and link takes up at least 1 inode.
- Large directories and large files can sometimes take up more than 1 inode.
For each kind of quota, filesystems have two different kinds of limits – hard and soft limits where the soft limit, if present, is less than or equal to the hard limit. When one is above the hard limit, the filesystem prevents consuming more blocks/inodes and may restrict what changes can be done to existing blocks/inodes until one drops below the soft limit. When one is above the soft limit but below the hard limit, a timer starts giving the user/project a certain grace time to drop below the soft limit again. Before the grace time expires, the user/project is not restricted so long as they stay below the hard limit. If the grace time expires without dropping below the soft limit, the filesystem restricts the user/project the same as exceeding the hard limit until the usage drops below the soft limit. Often a warning is printed to stderr when the soft limit is first exceeded.
Essentially, the soft limit is the value one must stay below but one may briefly exceed the soft limit without problems so long as one does not exceed the hard limit.
The grace time is currently 2 weeks on all data stores.
Some data stores do not support soft limits. On these filesystems, one must be more careful since there will be no warning message until one hits the hard limit where using more blocks/inodes fails outright.
Quota Pages
The different quota sub-topics are covered in the pages below