23.1 Understanding Space Quotas

You can control how space is allocated in an NSS pool or volume by restricting the amount of space available to a particular volume, directory, or user. These space restrictions, or quotas, work independently, with the lower value being the most restrictive if all constraints apply. NSS allocates the space as it is needed; the quota does not reserve the space.

If you set a quota to a value equal to or less than the current size of space in use for the specified volume, directory, or user, users cannot add files until enough files are deleted to free up space in the volume, directory, or user files. Users can continue to access existing files for which they are authorized users, but they cannot save them.

Quotas restrict the actual physical space that the volume, directory, or user is allowed to consume. When enforcing quotas, NSS considers only the actual physical blocks consumed (in 4 KB blocks), not the file’s logical size. If you have sparse files or compressed files, only the actual physical space they consume is counted against the quota. In order for a compressed file to be uncompressed, there must be enough space available in the most restrictive of the quotas set (whether volume, directory, or user) to accommodate the decompression process and the uncompressed file size. Otherwise, the user is not able to open the file. For more information about the space requirements for compressing and decompressing files, see Section 22.1.5, Factors Affecting Decompression.

As the amount of space consumed by a user’s files approaches the user’s space quota, the user should use caution when saving files. Data loss can occur if the user attempts to save a file that is too large for the remaining unused space.

To get the correct disk utilization information, use NSSMU or nsscon /SpaceInformation. For NSS volume, used space = in-use space + purgeable space. If you use df-h command or any other non-NSS utility to get the disk utilization information, the output may confuse the user as it shows only in-use space and does not take account of purgeable space.

WARNING:If storing a file would cause a quota to be exceeded, only part of the file is actually saved, resulting in data corruption.

If the Salvage attribute is enabled for a volume, deleted files are not immediately purged from the volume. Deleted files on the volume are not counted against quotas.

Volume Quotas

When you create an NSS volume, you have the option of setting a space quota for the volume or letting it grow to the size of the pool. At any time thereafter, you can view and configure the volume quota from the Storage > Volumes > Properties > Attributes tab in iManager. For information, see Section 23.2, Managing NSS Volume Quotas.

If you set a volume quota to grow to the pool size, you can also add segments to the volume’s pool to expand its size, and therefore, expand the volume quota.

As a volume nears its quota, automatic controls can be configured to manage space. For information, see Section 29.3, Monitoring Quotas and Space Usage for NSS Pools and Volumes.

Directory Quotas

Directory quotas limit the space available in an individual NSS directory. To use directory quotas on an NSS volume, you must first enable the Directory Quotas attribute.

For information about configuring attributes when you create a volume, see Understanding Volume Properties.

For information about setting directory quotas, see Section 23.3, Managing Directory Quotas

User Space Quotas

User space restrictions limit the space available to a user of the NSS volumes across all directories and files owned by the user. For information about setting user space quotas, see Section 23.4.3, Configuring a User Space Quota.

You must first enable the User Space Quotas attribute on the NSS volume where you want to configure user space restrictions. You can set the attribute at any time. For information about configuring the User Space Quotas attribute for an existing volume, see Modifying Attributes of an NSS Volume.

Example of Directory and User Space Quotas

Quotas are beneficial for systems where you want to control how your storage resources are used. In environments such as a university, where you set up a common work area for a large number of students and you want to limit the space that directory can consume, set a Directory Quota. You might also limit the amount of space an individual user’s work can consume by setting the User Quota.

For example, if a directory’s quota is 500 MB and the user’s quota is 1 GB, the user is limited to up to 500 MB in the specific directory. If the user can access multiple directories, each with a 500 MB quota, the maximum space the user’s work can consume for all directories combined is limited to the user’s 1 GB administrative limit.