Miscellaneous Administration Topics

8/14/2019 Miscellaneous Administration Topics

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Chapter 8: Miscellaneous

Administration

1

Presented by Scott Whigham


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Overvie

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Moving andCopying Databases

Dealing withOrphaned Users

CLR and .NETAssemblies M

an

agement Resource

Governor Policy-Based

Management

Powershell

FILESTREAM

Snapshots

What Were Going to Cover


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Chapter 8 covers several unrelated topics All essential to being a DBA

None large enough to warrant a full chapter

Chapter Introduction


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There are several techniques for movingand copying databases

BACKUP and RESTORE

DETACH and ATTACH

SQL Server Integration Services

Copy Database Wizard

Moving and Copying Databases


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Depending on which technique you us,you can copy and move:

On the same server

Onto multiple servers

Multiple databases at the same time



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In the next few videos, well seeexamples of how to move and copy

databases using the following

techniques: BACKUP and RESTORE

DETACH and ATTACH

SQL Server Integration Services

Copy Database Wizard



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Administration

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Way back in Chapter 5 (security) wetalked about how user accounts are

related to logins via the security

identifier (SID) Not by name

Orphaned Users


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User accounts that previously had a loginbut now have no associated login are

called orphaned users

Orphans can be created: By deleting logins

By copying/moving database to new instance

Orphaned Users


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1. When you delete a login, theassociated users are not deleted

Orphaned Users


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2. When you copy/move a database to adifferent instance, the user accounts

may be orphaned

If the destination instance does not have loginsfor the user account SIDs, the user accounts

will be orphaned

If the destination has logins with the expected

SIDs, the user accounts will be mapped

Orphaned Users


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Windows authentication logins: If your user accounts are built on Windows

user/group authentication logins, just create the

Windows authentication login in the SQL Server

Remember from Chapter 5 that the SID is the actual

Windows SID therefore the login/user will be mapped

automatically

Orphaned Users


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SQL Server authentication logins: For SQL Server authentication login-based user

accounts, simply creating the login with the

expected name wont work

CREATE LOGIN generates a random SID

Later on, well cover how to fix!

Orphaned Users


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You will encounter this problem often The user accounts are stored in the database but

logins are not

Any time you copy/move a database, you have to

deal with this issue

Orphaned Users


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Well talk about how to identifyorphaned users and strategies for

resolving

In the next video


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Administration

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There are several ways to identifyorphaned users

1. sp_change_users_login stored proc

2. Query the sys.database_principals view to locateusers with no matching sid in

sys.server_principals

3. Use SSMSs graphical tools

How to Identify Orphaned Users


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There are two solutions to this problem:1. Use sp_change_users_login stored procedure

2. Script out the login complete with SID from the

source server and run script on destination

server

Orphaned Users


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Lets take a look at usingsp_change_users_login and scripting

techniques!

Lets demo!


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Administration

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Introduction Moving and

Copying Databases



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SQL Server 2008 allows you to load .NETDLLs (called assemblies) into your

databases

Assemblies can be written in any language thatimplements that .NET Common Language Runtime

(CLR)

C#, Visual Basic, etc

Often called managed code or managed assemblies

CLR Assemblies


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An assembly loaded into SQL Server cancontain one or more:

Stored procedures

User-defined functions Triggers and more

CLR Assemblies


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Why would we need to use CLRassemblies?

Mostly because certain operations are more

efficient in .NET than Transact-SQL Examples: string manipulation, regular expressions

Secondly because .NET can do things Transact-SQL

cannot do

Example: create table results containing file and folderinfo

CLR Assemblies


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What does this have to do with the DBA? As the gate keeper, you must decide whether to

allow and, if you do allow, to what extent you

allow CLR integration

Remember the Principal of Least Privilege! http://learnitfirst.com/go.aspx?id=LPSX

CLR Assemblies


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CLR integration is disabled by default Enabled using the sp_configure stored proc

CLR Assemblies


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-- To view setting:EXEC sp_configure 'clr enabled'

-- run_value = 1: enabled

-- To enable:

EXEC sp_configure 'clr enabled', 1

GORECONFIGURE WITH OVERRIDE

CLR Assemblies


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Well talk about permission sets and howto configure security for CLR objects

In the next video


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Administration

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Once you enable SQL CLR, you mustdecide which permissions to allow

When you install an assembly, you must

determine its Host Policy Level SAFE

EXTERNAL_ACCESS

UNSAFE

CLR Assemblies


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SAFE is the default and most secure Cannot go outside the SQL Server process

Can connect to SQL Server in-process

SAFE


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EXTERNAL_ACCESS is SAFE plus go outof process

Can do all that SAFE can do

Can also go outside the SQL Server process toaccess external resources

Read files and folders

Read environmental variables

Read registry

more

EXTERNAL_ACCESS


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As a DBA, you cannot know every nuanceof every language that can write

managed code assemblies

Must coordinate with developer tounderstand security needs

How do I know which to use?


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Each permission set has differentrequirements for creation:

SAFE: requires CREATE ASSEMBLY permissionin the database

EXTERNAL_ACCESS: SAFE plus EXTERNALACCESS ASSEMBLY server permission

UNSAFE: sysadmins only!



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Create assembly in the [LearnItFirst.com]database

USE [LearnItFirst.com]GO

CREATE ASSEMBLY LIFRegEx

FROM C:\MyAssembly.DLL

WITH PERMISSION_SET = SAFE



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Can change permission set with ALTERASSEMBLY

ALTER ASSEMBLY LIFRegEx

WITH PERMISSION_SET =

EXTERNAL_ACCESS



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With respect to the CLR, the DBA isexpected, at a minimum, to be able to:

To be able to explain what the CLR is

To be able to make suggestions related to when touse the CLR for certain operations

To be able to stop developers from using CLR

unnecessarily

To understand the various permission sets

The DBAs Role


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To reiterate: you are not expected toknow every single language

Dont be intimidated by the CLR

If a manager tells you that, You have to know C#to be a good DBA during a job interview, you do

not want to work for that person!

.. Well, how much does it pay again?

The DBAs Role


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The Resource Governor: New in SQL 2008

Allows you to limit resources

based on certain criteria

CPU, memory, number of

requests, more

Only available in Enterprise

and Developer editions

The Resource Governor

img by eliburd @ flickr.com

l


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Examples uses of the Resource Governor Can prevent expensive queries from consuming

more than an allowed amount of memory or CPU

Limit the amount of CPU that backup compression

can consume Ensure that specific applications cannot issue

queries or workloads that are unhealthy to the restof the server

Web host wants to provide guaranteed levels ofservice to multiple clients

Example Usage

l


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The basics of how it works:1. DBA creates a resource pool

2. DBA assigns the resource pool one or more

workload groups

3. DBA writes a classifier function that binds

incoming sessions to the appropriate workload

group

Example Usage

Th R G


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The Resource Governor

Source: Using the Resource Governor, white paper, Microsoft 2009


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Workload groups allow more granularsettings

Workload Groups

W kl d G


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Settings available for workload groups: 0 means unlimited for all

Maximum Requests

Max number of simultaneous requests

CPU Time (sec)

Max amount of CPU time that a request can use

Memory Grant %

Max amount of memory a single request can take from the pool

Grant Time-out (sec)

Max time that a query can wait for a resource before the query fails

Degree of Parallelism

Max degree of parallelism for parallel requests. Range is 0 to 64

Workload Groups


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The Classifier F nction


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The classifier function: There can be only one

If it returns NULL or a non-existent group, the

session is bound to the defaultworkload group

Sessions are bound to the workload group for life

The Classifier Function

Putting It All Together


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After enabling the Resource Governorand putting a classification function in

place:

1. User logs in2. The login authentication is verified

3. Upon successful authentication, any LOGON

triggers are executed

4. Finally, classification occurs

Putting It All Together

Words of Wisdom


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A final word of caution Be ready

If you mess up your classifier function, youve messed

up the entire server

Only Dedicated Administrator Connection (DAC)sessions can bypass classification

If a problem arises, log in as DAC and remove classifier

Words of Wisdom

Lets play!


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In the next video, lets play with theResource Governor!

Let s play!


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Administration

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What We re Going to Cover

Policy Based Management


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Windows administrators have long beenfamiliar with policy-based management

All user accounts must change their password

every 42 days and it must contain letters, numbers,

and special characters

Policy-Based Management



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DBAs have always had standards andbusiness rules

All stored procedures must begin with usp_

No database may have AutoShrink turned on However, what we havent had is a way to

enforce them automatically




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SQL Server 2008 introduces Policy-BasedManagement (PBM)

Allows DBA to define business rules (i.e.policies)

that can either be:

Automatically enforced by SQL Server (i.e. prevent non-

compliant modifications)

Reported to the DBA as non-compliant




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Nearly all DBAs have a daily task list: Verify backups

Look for anomalies (low disk space, unrecognized

files or folders, etc)

Check the error logs

Check the job logs

and many more tasks




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One such task is to verify that newservers are compliant

Example: Have any new servers been installed?

If Yes, are they up to our standards?

Evaluation or Developer Edition only unless installed by DBAs

(to ensure licensing compliance)

Minimum build number

MYDOMAIN\SQLDBAsWindows group is sysadmin

Authentication mode is Windows-only (a.k.a. Integrated)




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Another task is ensuring no changes haveoccurred that result in databases/objects

being non-compliant

Are all production databases Online

Using correct recovery model

Are there any new [tables/views/functions/procs]?

Do they meet naming conventions?




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Manual enforcement of these types ofpolicies is error prone and a time sink

Spending just 10 minutes a day on manually

enforcing policies adds up to more than 40 hours

at the end of a year

An entire work week!

How much time did you have to spend during the

yearfixing a problem that occurred because ofnon-compliance?


In the next video


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Well take a look at the terms andconcepts behind SQL Server 2008s PBM

In the next video


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Administration

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Overview Chapter

Introduction




anageme

nt Resource


Management

Powershell

FILESTREAM Snapshots

What We re Going to Cover



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Understanding SQL Servers policy-basedadministration is

Easy because we are all familiar with the basic

ideas behind policy-based management

Difficult due to having to learn new abstraction-

layer-type terms




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First, lets talk about what you can police: Nearly anything that has properties

Okay, so what items in SQL Server have

properties? Everything

y g



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Are you saying that I can create a policyon anything I want?

Pretty much!

What cant I police? Anything you would normally do in a constraint or

trigger

Anything you would normally do with Resource

Governor

y g


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It only takes two steps to define yourpolicies:

Step 1: Create a condition

Step 2: Create thepolicybuilt on the condition

y g



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Conditions define what you want topolice

I want to ensure that all stored procedures in

our WebMarketing database start with usp_

No database may have AutoShrink turned on

This may seem like the policy but

y g



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Policies define the action you want tooccur when a set of conditions is met

A developer should receive an error if they try to

create a stored procedure in our WebMarketing

database that does not start with usp_

y g



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A (weak?) analogy: Conditions are like SELECT statements

Rows that are returned from running the query are

compliant

SELECT * FROM sys.procedures

WHERE name LIKE 'usp_%'



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So far, so good, right? Nothing too difficult yet

Lets make things a bit more complicated in the

next video!


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Administration

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Overview Chapter

Introduction




anageme

nt Resource


Management

Powershell




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In truth, PBM is quite easy The tricky parts are:

Understanding terms likefacet,property, and

target Understanding which facets allow which

evaluation modes

Writing conditions and always being positive


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Each facet contains at least oneproperty Properties have values

To retrieve or query a propertys value,

you write an expression



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Example facet: The Stored Procedurefacet has several properties:

Name

CreateDate

Schema



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To continue our previous analogy in

which a condition was similar to a SELECT

statement

Think of the facet as what occurs after the FROM Think of the property as the column



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Consider this query:

SELECT * FROM sys.procedures

WHERE name LIKE 'usp_%

In this example, sys.procedures wouldrepresent the Stored Procedure facet andname would represent the facets Nameproperty



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We write our conditions against facets

Our desired condition: All stored procedures in

the WebMarketing database must begin with

usp_

Which two facets will we use?

1. _________________________

2. _________________________



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We write our conditions against facets

Our desired policy: All stored procedures in the

WebMarketing database must begin with usp_

Which two facets will we use?

1. Stored Procedure

2. Database



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Explanation:

Stored procedure is the facet and we must find

all stored procedures whose Name property starts

with usp_

Database is the facet and we must find only thatdatabase whose name is WebMarketing

In the next video


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Well learn more about expressions and

the mindset of writing conditions and

policies


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Expression syntax is not difficult

Operators are same as C#: ==, !=, etc

Functions are similar to C# and T-SQL:

GETDATE() returns current system date/time

ISNULL() returns true/false to indicate if an expression is

null

Conditions are similar to Transact-SQL

LIKE and NOT LIKE, IN and NOT IN

Double-quotes around strings



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Expression syntax is used in the graphical

tools only

If you want to script out your conditions, you must

write XML!


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Policies also have Categories (a.k.a. Policy

Groups)

Can run the entire category against a

database/server instead of one-policy-at-a-time

Can mandate that new databases participate


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Overview Chapter

Introduction




anageme

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Management

Powershell


Evaluations


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Anytime a policy is evaluatedand finds

non-compliance, it logs the offender

In the SQL Server error Log

In the Windows Application log

In the msdb database

Be prepared for msdb growth!

Execution Modes


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Policies also have Execution Modes which

determine

When the policy will be evaluated

The response to non-compliance

Execution Modes


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There are four execution modes:

On demand

On schedule

On change: prevent

On change: log only

Not all facets support all execution modes

Execution Modes


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On demand: policies are not evaluated

unless manually done so by admin

Useful for audits and non-critical policies

Supported by all facets

Actions taken:

Raises error #34052

Logs infraction

Execution Modes


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On schedule: a SQL Server job is createdthat periodically evaluates the policy Useful when evaluation performance impacts

system

Supported by all database-engine facets

Job does not error out if policy violations found

Writes errors to the logs and evaluation history

Actions taken:

Raises error #34052

Logs infraction

Execution Modes


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On change: log: logs non-compliance

only

Useful when you want a history of policy

Supported by few facets

Actions taken:

Logs infraction

Execution Modes


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On change: prevent: non-compliance is

not allowed

Useful to prevent critical changes

Expensive

Supported by fewest facets

Actions taken:

Rolls back user transaction

Raises error #34050 or #34051

Logs infraction

Summary


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Facet On change: log On change: prevent

Application Role a a

Asymmetric Key a a

Database Option a

Database Role a a

Login Options a a

Resource Pool a a

Schema a a

Server Configuration a

Stored Procedure, Functions, Views a a

Table Options a a

Workload Group a a


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Writing Policies and Conditions


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If you want to prevent someone who is

not a sysadmin from adding a database,

then this is apermission

If you want to report on the databasesthat are currently not owned by

sysadmins, then you want apolicy



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Do policies take the place of permissions

in SQL Server 2008?

No!

Policies and permissions actually have nothing to

do with one another



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Generally speaking, actions that can be

prevented by permission are not

preventable using On change: prevent

Example: preventing someone from creating

databases, tables, procs, etc



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Prevention policies are things you have

permission to do but, for some reason,

management doesnt want you doing

them

Such as creating stored procs in the

WebMarketing database that do not start with

usp_



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Remember our policy: We want all

stored procedures in WebMarketing to

start with usp_

Is this a permission or a policy?

A policy however the user still needs the CREATE PROC

permission in the database!

In the next video


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Well discuss how to write effective

conditions and policies


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Administration

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Overview Chapter

Introduction



CLR and .NETAssemblies Ma

nagement Resource

Governor

Policy-BasedManagement

Powershell



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Example policy requirement: All

databases must be owned by the sa

This requires one condition since there is only one

facet (Database facet)



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How would you write the condition?

1. To return databases owned by the sa

2. To return databases not owned by the sa



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How would you write the condition?

To return databases owned by the sa

To return databases not owned by the sa

Your conditions define the ideal, not the

exception

Since we want only sa-owned databases,our condition is where @Name=sa


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We have the choice of writing our Stored

Procedure condition so that it returns:

Stored procs that start with usp_

Stored procs that do notstart with usp_

Which do we choose?



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We have the choice of writing our Stored

Procedure condition so that it returns:

Stored procs that start with usp_

Stored procs that do notstart with usp_

Remember we want our conditions to

define what we do want, not what we

dont want



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To understand why it is this way, consider

our options for the second facet

(Database facet):

Database named WebMarketing

Databases not named WebMarketing

Clearly we choose the first option



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The final step is to create a policy on these two

conditions


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Overview Chapter

Introduction




nagement Resource

Governor


Powershell


PowerShell!


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PowerShell support for SQL Server 2008 is

included in SSMS

PowerShell is a very extensible and

powerful scripting shell that allowsadmins to script (automate)

administration functions

PowerShell!


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If you know DOS, you can easily get

started with PowerShell (PS)

Commands like dir, del, cd perform the same

function in PS

PowerShell can do everything you can do

at the command line and more

PowerShell!


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So why talk about PowerShell in a SQL

admin course?

SQL DBAs can automate SQL Server via PowerShell

scripts!

This allows for uniformity across the enterprise

Anyone who knows PowerShell can write scripts

Allows integration between systems - can load Windows

Event Logs into SQL Server tables for analysis via PS

PowerShell!


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You can manage your SQL Server by

Issuing PS commands directly into the PS shell

(powershell.exe)

Executing PS files that contain PS scripts

C:\Scripts\DeployNewServer.ps1

Creating SQL Server jobs that execute PowerShell

steps

PowerShell!


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Full coverage of PS is beyond the scope of

this course however there are several

concepts you will need to know

Lets start with the basics

PowerShell!


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PowerShell and the OS:

Included in Windows 2008 and Windows 7

Download for Windows 2003, Vista, XP, etc

Versions of PowerShell

2.0 - Windows 2008 R2 and Windows 7

1.0 - Windows 2008, Windows 2003, Vista, XP

http://www.microsoft/powershell

PowerShell!


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SQL Server 2008 ships

with the sqlps.exe, a

minishell

Can drop to command line

and just run sqlps to

manage servers

Integrated into SSMS

PowerShell!


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The sqlps minishell incorporates several

cmdlets for managing SQL Server

Pronounced commandlets

cmdlets are .NET classes invoked by

PowerShell at runtime

Common cmdlets included in sqlps:

Invoke-Sqlcmd

Invoke-PolicyEvaluation

In the next video


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PowerShell is easier to demo than talk

about!


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Overview Chapter

Introduction




nagement Resource

Governor


Powershell


Unstructured Data


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Lets compare data storage/access of

1990 to 2010 for a health insurance

company

1990: Storage: DB2

Tables to store an insured family: 25

Type of data stored: row data only

Export formats: CSV, text

Unstructured Data


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2010:

Storage: SQL Server 2008

Tables to store an insured family: 50

Type of data stored: row data, xml, images, audio

Export formats: CSV, text, xml, images, audio

Unstructured Data


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Todays companies have to deal not just

with row data but unstructured data as

well

Legal firms need transactional support for MS

Word, Excel documents

Health industry needs transactional support for

imaging

Music industry needs transactional support foraudio


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Unstructured Data


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Files are stored in a folder in the file

system that requires additional

permissions

Unstructured Data


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Beginning in SQL Server 2005, we could store

unstructured data in the form of files in anew data type, VARBINARY(MAX)

Replaced the older image data type

Pros: transactional support, simplify backup/restore,native SQL Server security, never stale, can separate

storage using filegroups

Cons: speed, data must be converted in/out to binary

format, limited to 2GB files, explosion of databasegrowth, buffer pool memory used to access data

Unstructured Data


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Files are stored in a VARBINARY(MAX)

column as a Binary Large Object (BLOB)

Unstructured Data


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SQL Server 2008 introduces FILESTREAM

access

Sort of a blend of file system pointers and

VARBINARY(MAX) techniques

Data is stored in the NTFS filesystem Improved speed, separation of storage

All data access is through SQL Server

Single point of security, full transactional support, full-text indexing, no stale links


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Unstructured Data


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More about FILESTREAM:

Works in all editions

Allows full ROLLBACK support

Supported on clusters and in log shipping

No limit on file size

VARBINARY(MAX) is limited to 2GB

VARBINARY(MAX) FILESTREAM has no such limit

In the next video


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Well cover more DBA-related details

about FILESTREAM


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Overview Chapter

Introduction




nagement Resource

Governor


Powershell


FILESTREAM


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To use FILESTREAM for a database, follow

these five steps:

1. Enable FILESTREAM for the instance

2. Add a FILESTREAM-enabled filegroup to the

database

3. Add one or more files to the new filegroup

4. Create your column and assign it the FILESTREAM

attribute5. Load your data!

FILESTREAM


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these five steps:



database




FILESTREAM


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FILESTREAM requires

both SQL Server DBA

and the Windows

admin

The SQL Server Service

must be configured for

FILESTREAM access first

using the SQL ServerConfiguration Manager

d

FILESTREAM


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Inside SQL Server, FILESTREAM is an

instance-level option

Disabled by default; sysadmins only can change

T bl FILESTREAM i T t

FILESTREAM


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To enable FILESTREAM using Transact-

SQL:

EXEC sp_configure filestreamaccess level

-- 0: disabled (default)-- 1: Transact-SQL access only

-- 2: Full access enabled (a.k.a.

-- T-SQL and streaming access

-- via Windows APIs)-- NOTE: Local disks only for now

T FILESTREAM f d b f ll

FILESTREAM


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these five steps:



database




O bl FILESTREAM t th i t

FILESTREAM


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Once you enable FILESTREAM at the instance

level, you must now:1. Create a new filegroup specifically for FILESTREAM

2. Add files to the filegroup

You can do this with CREATE DATABASE orALTER DATABASE

Enable FILESTREAM on a

Database


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Database


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Database


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To add FILESTREAM to an existing

FILESTREAM


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To add FILESTREAM to an existing

database:

ALTER DATABASE [LearnItFirst.com]

ADD FILEGROUP FilestreamFG

CONTAINS FILESTREAM

GO

ALTER DATABASE [LearnItFirst.com]

ADD FILE(Name=File1,

FileName=F:\File1)TO FILEGROUP = FilestreamFG


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Administration

174




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Overview Chapter

Introduction




nagem

ent Resource

Governor


Powershell


To use FILESTREAM for a database follow

FILESTREAM


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these five steps:1. Enable FILESTREAM for the instance


database




You can add FILESTREAM support to new tables

FILESTREAM


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You can add FILESTREAM support to new tables

or existing tables Use ALTER TABLE to add to an existing table

USE [LearnItFirst.com]GOCREATE TABLE dbo.ClaimImage (

ClaimId INT NOT NULL PRIMARY KEY, TheImage VARBINARY(MAX) FILESTREAM NOT NULL, RowId UNIQUEIDENTIFIER NOT NULL

ROWGUIDCOL UNIQUE DEFAULT NEW_ID())

-- Tables with FILESTREAM data must have a-- non-null UNIQUEIDENTIFIER column

To use FILESTREAM for a database follow

FILESTREAM


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these five steps:1. Enable FILESTREAM for the instance


database




Writing/reading binary data is for

FILESTREAM


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Writing/reading binary data is for

developers Requires accessing Win32 APIs

.NET is popular but can write Transact-SQL directly

INSERT dbo.ClaimImage (ClaimId, TheImage)

VALUES (1, 0x01)

DBAs needs to know about security and

FILESTREAM


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DBAs needs to know about security and

backup/recovery Security permissions are done inside SQL Server,

not on the file system

The physical files/folders are secured by SQLServer service account

Backup/restore will include all files

Best Practices for FILESTREAM

FILESTREAM Best Practices


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Best Practices for FILESTREAM

Do not make your ROWGUIDCOL a clustered index For best performance, FILESTREAM files should be on

separate physical volumes when possible

NEWSEQUENTIALID() will perform better than NEWID()when replicating databases

Read Paul Randalls column: http://learnitfirst.com/go.aspx?id=WBLX

Have your network admins (or whoever configures thephysical Windows Server 2008/2003 machine) read

the top part of this article: http://msdn.microsoft.com/library/dd206979.aspx

Final thoughts

FILESTREAM
http://learnitfirst.com/go.aspx?id=WBLXhttp://msdn.microsoft.com/library/dd206979.aspxhttp://msdn.microsoft.com/library/dd206979.aspxhttp://learnitfirst.com/go.aspx?id=WBLX


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p 182

Final thoughts

Transact-SQLs DELETE statement causes the

physical file to be deleted

Physical file deletion is not performed until a

CHECKPOINT operation

Do not attempt to manage files via the file system

Cannot change names, attributes or delete files

There are other options

Search for SQL Server 2008 remote BLOB storage


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Administration

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Overview Chapter

Introduction




nagem

ent Resource

Governor


Powershell


A database snapshot is a read-only

Database Snapshots


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A database snapshotis a read-only

copy of a database that stops at thepoint the snapshot is taken

Example: If you take a snapshot of the LearnItFirst

database at 0800, the snapshot would have theentire database yet would not reflect any changes

that occurred after 0800


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Database Snapshots


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-- At 0800, we execute:CREATE DATABASE LIFSnapshot_0800

ON(NAME=LearnItFirst

,FILENAME=D:\LIF_0800.ss)AS SNAPSHOT OF LearnItFirst

-- Logical file name must be

-- same as source. Also note-- that we do not define a log


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Reads against the snapshot:

Database Snapshots


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Reads against the snapshot:

Will use the source database if the data requested

has not changed since snapshot creation

Acquire SHARED locks at source to prevent blocking

Will return the snapshot copy if the data haschanged

This provides a at creation level of consistency to data


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Example restore:

Database Snapshots


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Example restore:

-- Only allowed if:

-- (1) there is only one snapshot

-- (2) all source db files exist

RESTORE DATABASE LearnItFirst

FROM DATABASE_SNAPSHOT =

LIFSnapshot_0800

Database snapshots use sparse files to

Database Snapshots


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atabase s aps ots use spa se f es to

minimize disk space Feature of NTFS that allows NTFS to allocate disk

space on an as needed basis

When you create a snapshot, database pages arenot copied to the snapshot

As pages become dirty, the original data page iscopied to database snapshot

When that happens, the sparse files size stays the sameyet the Size on disk increases

A 1.1GB database with a fresh snapshot

Database Snapshots


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A 1.1GB database with a fresh snapshot


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Final thoughts

Database Snapshots


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g

Pros: Great way to provide users with a point-in-time view of

database

Snapshots are quick and easy to create thanks to sparse files

Cons: No way to create using SSMS graphical tools; T-SQL only

Cannot change user permissions for snapshot vs. source

A snapshot is a read-only copy of the source

Documents

Miscellaneous Administration Topics