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Oracle® ZFS Storage Appliance Administration Guide
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Document Information

Using This Documentation

Chapter 1 Oracle ZFS Storage Appliance Overview

Chapter 2 Status

Chapter 3 Initial Configuration

Chapter 4 Network Configuration

Chapter 5 Storage Configuration

Chapter 6 Storage Area Network Configuration

Chapter 7 User Configuration

Chapter 8 Setting ZFSSA Preferences

Chapter 9 Alert Configuration

Chapter 10 Cluster Configuration

Chapter 11 ZFSSA Services

Chapter 12 Shares, Projects, and Schema

Understanding Shares

Storage Pools

Using Shares

Share Properties

Share Snapshots

Share Clones

Shares Space Management

Shares Space Terminology

Understanding Snapshots

File System and Project Settings

Data Quotas

Data Reservations

Space Management for Replicating LUNs

User and Group Settings

Viewing Current Usage

Viewing Current Usage in the BUI

Viewing Current Usage in the CLI

Setting User or Group Quotas

Set User or Group Quotas Using the BUI

Set User or Group Quotas Using the CLI

Identity Management

Filesystem Namespace

Namespace Nested Mountpoints

Namespace Protocol Access to Mountpoints

Namespace NFSv2 / NFSv3

Namespace NFSv4

Namespace SMB

Namespace FTP / FTPS / SFTP

Namespace HTTP / HTTPS

Shares > Shares

Working with Shares > Shares in the BUI

List of Shares

Editing a Share

Usage Statistics

Static Properties

Shares Project Panel

Creating a Share

Working with Shares > Shares in the CLI

Navigation

Share Operations

Shares > Shares CLI Properties

Shares > Shares > General - BUI Page

Space Usage

Volume Size

Thin Provisioned

Mountpoint

Read only

Update access time on read

Non-blocking mandatory locking

Data deduplication

Data compression

Checksum

Cache Device Usage

Synchronous Write Bias

Database Record Size

Additional Replication

Virus Scan

Prevent Destruction

Restrict Ownership Change

Custom Properties

Shares > Shares > Protocols - BUI Page

Shares Protocols

Share Protocols - NFS

Share Protocols - CLI

Security Modes

Character Set Encodings

Shares - SMB

Shares - iSCSI

Shares - HTTP

Shares - FTP

Shares - SFTP

Shares > Shares > Access

Access Control

Shares - Root Directory Access

Shares - User

Shares - Group

Shares - Permissions

Shares - ACL Behavior

ACL Behavior on Mode Change

ACL Inheritance Behavior

Root Directory ACL

Shares - Snapshots

Shares - Snapshot Properties

.zfs/snapshot visible

Scheduled Snapshot Label

Listing Snapshots Using the BUI

Manual Snapshots Using the BUI

Create a project level snapshot

Create a share/LUN level snapshot

Renaming a Snapshot (BUI)

Destroying a Snapshot (BUI)

Rolling back to a Snapshot (BUI)

Cloning a Snapshot (BUI)

Scheduled Snapshots Using the BUI

Manual Snapshots Using the CLI

Listing Snapshots (CLI)

Taking Manual Snapshots (CLI)

Renaming a Snapshot (CLI)

Destroying a Snapshot (CLI)

Rolling back to a Snapshot (CLI)

Cloning a Snapshot (CLI)

Listing Dependent Clones Using the CLI

Scheduled Snapshots Using the CLI

Setting the Scheduled Snapshot Label Using the CLI

Projects

Working with Projects Using the BUI

Project Fields

Editing a Project

Usage Statistics

Static Properties

Creating Projects

Working with Projects Using the CLI

Navigation

Project Operations

Selecting a Pool in a Cluster

Project Properties

Project - General

Project - General Properties

Project - Space Usage

Project - Quota

Project - Reservation

Project - Inherited Properties

Project - Custom Properties

Filesystem Creation Defaults

LUN Creation Defaults

Project Protocols

Project Access

Project Snapshots

Project Snapshot Properites

.zfs/snapshot visible

Scheduled Snapshot Label

Schemas

Customized Share Properties

Working with Schemas in the BUI

Configuring a Schema Using the BUI

Working with Schemas Using the CLI

Configuring a Schema Using the CLI

Chapter 13 Replication

Chapter 14 Shadow Migration

Chapter 15 CLI Scripting

Chapter 16 Maintenance Workflows

Chapter 17 Integration

Index

Understanding Snapshots

Snapshots present an interesting dilemma for space management. They represent the set of physical blocks referenced by a share at a given point in time. Initially, this snapshot consumes no additional space. But as new data is overwritten in the new share, the blocks in the active share will only contain the new data, and older blocks will be "held" by the most recent (and possibly older) snapshots. Gradually, snapshots can consume additional space as the content diverges in the active share.

Some other systems will try to hide the cost of snapshots, by pretending that they are free, or by "reserving" space dedicated to holding snapshot data. Such systems try to gloss over the basic fact inherent with snapshots. If you take a snapshot of a filesystem of any given size, and re-write 100% of the data within the filesystem, by definition you must maintain references to twice the data as was originally in the filesystem. Snapshots are not free, and the only way other systems can present this abstraction is to silently destroy snapshots when space gets full. This can often be the absolute worst thing to do, as a process run amok rewriting data can cause all previous snapshots to be destroyed, preventing any restoration in the process.

In the Sun Storage 7000 series, the cost of snapshots is always explicit, and tools are provided to manage this space in a way that best matches the administrative model for a given environment. Each snapshot has two associated space statistics: unique space and referenced space. The amount of referenced space is the total space consumed by the filesystem at the time the snapshot was taken. It represents the theoretical maximum size of the snapshot should it remain the sole reference to all data blocks. The unique space indicates the amount of physical space referenced only by the current snapshot. When a snapshot is destroyed, the unique space will be made available to the rest of the pool. Note that the amount of space consumed by all snapshots is not equivalent to the sum of unique space across all snapshots. With a share and a single snapshot, all blocks must be referenced by one or both of the snapshot or the share. With multiple snapshots, however, it's possible for a block to be referenced by some subset of snapshots, and not any particular snapshot. For example, if a file is created, two snapshots X and Y are taken, the file is deleted, and another snapshot Z is taken, the blocks within the file are held by X and Y, but not by Z. In this case, destroying Z will not free up the space, but destroying both X and Y will. Because of this, destroying any snapshot can affect the unique space referenced by neighboring snapshots, though the total amount of space consumed by snapshots will always decrease.

The total size of a project or share always accounts for space consumed by all snapshots, though the usage breakdown is also available. Quotas and reservations can be set at the project level to enforce physical constraints across this total space. In addition, quotas and reservations can be set at the filesystem level, and these settings can apply to only referenced data or total data. Whether or not quotas and reservations should be applied to referenced data or total physical data depends on the administrative environment. If users are not in control of their snapshots (i.e. an automatic snapshot schedule is set for them), then quotas should typically not include snapshots in the calculation. Otherwise, the user may run out of space but be confused when files cannot be deleted. Without an understanding of snapshots or means to manage those snapshots, it is possible for such a situation to be unrecoverable without administrator intervention. In this scenario, the snapshots represent an overhead cost that is factored into operation of the system in order to provide backup capabilities. On the other hand, there are environments where users are billed according to their physical space requirements, and snapshots represent a choice by the user to provide some level of backup that meets their requirements given the churn rate of their dataset. In these environments, it makes more sense to enforce quotas based on total physical data, including snapshots. The users understand the cost of snapshots, and can be provided a means to actively management them (as through dedicated roles on the ZFSSA).