Hard quotas (Disk and Files fields) impose a hard limit on system resources; any operation that would result in exceeding the limit fails. The soft quotas (Threshold, Soft Disk and Soft Files fields) enable you to receive a warning when users reach a certain resource level without affecting their data access, so you can take appropriate action before the quota is exceeded.
Threshold quotas (quotas specified using the Threshold field) are equivalent to quotas specified using the Soft Disk field.