HP Integrity BL860c Programmierhandbuch

Managing the System Registry Hive on

Windows Server 2003 and Windows Server

2008 Integrity Systems

Published: November 2009

Edition: 1.0, Part Number: 5992-5670

Table of Contents

About This Document.........................................................................................................5

Intended Audience.................................................................................................................................5

Typographic Conventions......................................................................................................................5

Technical Review....................................................................................................................................7

Introduction.......................................................................................................................................7

Understanding System Hive Fundamentals and Limits...................................................................7

Estimating System Hive Size.............................................................................................................8

Causes of Increasing System Hive Size...........................................................................................10

Breaching the System Hive Limit....................................................................................................10

Differences in Windows Server 2003, Windows Server 2008, and Windows Server 2008 R2.........10

System Recovery...................................................................................................................................11

General Outlines for Recovery........................................................................................................11

Booting WinPE/WinRE and Loading the System Hive Registry.....................................................11

Recovery Specifics: Windows Server 2003......................................................................................14

Recovery Specifics: Windows Server 2008......................................................................................15

Creating a Pseudo LastKnownGood System Registry Hive for Windows Server 2003 and

Windows Server 2008......................................................................................................................16

Using the Created Pseudo LastKnownGood (LKG).......................................................................19

Proactive Avoidance.............................................................................................................................20

Checking Disk Infrastructure..........................................................................................................20

Special Consideration for Symantec Veritas Volume Manager (SFW)............................................21

Working with the SAN Administrator for MPIO Optimizations and SAN Maintenance..............21

Introducing the HP Registry Monitor Service.................................................................................21

Installing the HP Registry Monitor Service.....................................................................................22

Configuring the HP Registry Monitor Service................................................................................22

Deciding Whether to Implement a Single ControlSet strategy.......................................................24

Optimizing the Hive........................................................................................................................24

Conclusion............................................................................................................................................24

Table of Contents 3

List of Figures

1 System Hive ControlSet structure...................................................................................................7

2 Select Key values.............................................................................................................................8

3 RegEdit Export screen.....................................................................................................................9

4 Directory listing showing difference in file size.............................................................................9

5 Command Prompt option in WinPE (HP Reinstall media)..........................................................12

6 Command Prompt option in WinRE.............................................................................................12

7 Loading the System Hive in WinPE (HP Reinstall media)...........................................................13

8 General tab....................................................................................................................................17

9 Triggers tab....................................................................................................................................18

10 Actions tab.....................................................................................................................................19

11 PowerShell screen..........................................................................................................................20

12 Error message................................................................................................................................23

4 List of Figures

About This Document

This white paper provides an explanation of the system registry hive and its limitations, and

gives some methods for managing those limitations. The opinions in this document may suit

some environments more than others.

Intended Audience

This document is intended for system architects and administrators responsible for managing

HP Integrity servers. Architects and administrators are expected to know operating system

concepts, commands, and configuration, as well as networking concepts and configuration. Some

manipulation of the system registry file is necessary, so a familiarity with the Registry Editor

application (RegEdit) is required. You should also be able to liaise with different departments

in your organization, such as the Storage Area Networks (SAN) group, specialist application

groups, and Change Management/Documentation departments.

This document is not a tutorial.

Typographic Conventions

This document uses the following typographical conventions:

%,$, or #A percent sign represents the C shell system prompt. A dollar sign

represents the system prompt for the Bourne, Korn, and POSIX shells.

A number sign represents the superuser prompt.

Command A command name or qualified command phrase.

Computer output Text displayed by the computer.

Ctrl+x A key sequence. A sequence such as Ctrl+x indicates that you must hold

down the key labeled Ctrl while you press another key or mouse button.

Key The name of a keyboard key. Return and Enter both refer to the same

key.

User input Commands and other text that you type.

Variable The name of a placeholder in a command, function, or other syntax

display that you replace with an actual value.

WARNING A warning calls attention to important information that if not understood

or followed will result in personal injury or nonrecoverable system

problems.

CAUTION A caution calls attention to important information that if not understood

or followed will result in data loss, data corruption, or damage to

hardware or software.

IMPORTANT This alert provides essential information to explain a concept or to

complete a task

NOTE A note contains additional information to emphasize or supplement

important points of the main text.

Intended Audience 5

Technical Review

Introduction

The Windows Server 2003 and Windows Server 2008 operating systems have a system registry

hive size limitation of 32 MB (for all Service Packs). For most customer configurations, it is

unlikely this limit will ever be reached. But in certain circumstances, particularly for customers

with large configurations or numbers of SAN disks using multipath MPIO technology, the 32

MB limit is reachable, and can cause the system to fail to boot when restarted.

HP and Microsoft have worked together to create methods of recovery, proactive notification,

and design avoidance should the System hive approach its 32 MB limit. By using proactive

notification and the other methods described in this white paper, reboot failures of this type can

be avoided.

Understanding System Hive Fundamentals and Limits

The System hive is a critical registry component. It is referenced by the Registry Editor application

(RegEdit.exe, or RegEdit) as “SYSTEM”. Below the System hive, structurally, are a number

of ControlSets. The origin of these ControlSets goes back to the Windows NT operating system.

A ControlSet encapsulates all of the system's hardware and software information, such as device

driver and SAN volume details, in a tree structure. Because this data is critical to system operation,

anytime the System hive is changed by adding a new hardware component or software package,

a new ControlSet is created.

Microsoft designed the system to maintain more than one ControlSet in order to achieve system

resilience. Typically there are two ControlSets, such as ControlSet001 and ControlSet002. The

system rotates between these two ControlSets every time a change is made. This functionality

allows an Administrator to revert back to the “Last Known Good Configuration”

(LastKnownGood, or LKG) by pressing the F8 key should the system fail to boot. Figure 1 shows

a typical System hive ControlSet, as displayed by RegEdit.

Figure 1 System Hive ControlSet structure

Note that Figure 1 shows ControlSet001 and ControlSet003. These numbers do not have to be

contiguous. There can even be more than two ControlSets in extreme circumstances, such as a

Technical Review 7

known failed ControlSet. For the purposes of this document, the CurrentControlSet key is

considered an exact replica or alias of one of the other ControlSets, and does not consume any

System hive space.

The other important key to note is the Select key, as shown in Figure 2.

Figure 2 Select Key values

In the Select key, the Current and LastKnownGood subkey values are critically important. In

Figure 2 you can see the values for both are “1”. If an application or hardware change had recently

occurred, the LastKnownGood value would be different than the Current value. Therefore, in

the example above, this means that ControlSet003 is actually superfluous and could theoretically

be deleted in order to gain space in the System hive.

IMPORTANT: If the system is running Windows Server 2003 for Itanium-based Systems, an

understanding of Select key values is critical for configuring the system to reduce the size of the

System hive.

Estimating System Hive Size

The System hive is essentially a database of keys that is stored on the filesystem of the boot drive

in the following location:

%SystemRoot%\System32\Config\SYSTEM

It is important to note that the size of the file does not necessarily reflect the size of that database.

This is because the System hive never shrinks under normal operation. For example, when 5 MB

of data is added to the System hive, its size grows by 5 MB (to a maximum of 32 MB). However,

if that same 5 MB of data is deleted from the hive, its file size does not change, even though that

space is now available for reuse. Therefore, a hive size of 32 MB does not necessarily mean that

much space is being utilized, and normal system operation can still proceed.

The easiest method to determine true hive size is to use RegEdit to save the System hive in binary

form. RegEdit has the ability to compact the System hive and remove any free space, thus reporting

its true size. Figure 3 shows the correct options for saving the System hive. Note the highlighted

fields.

Figure 3 RegEdit Export screen

In the example above, a new file is created called CompactedRegFile. Now, by examining the

file system, the size difference between the SYSTEM and CompactedRegFile files can be

determined. Figure 4 shows the output of a directory listing.

Figure 4 Directory listing showing difference in file size

The difference in this example is approximately 7 MB, indicating that roughly 35% of the System

hive is not being used. This unused space is consumed prior to any expansion of the actual file

size, so in the example above, 7 MB of data must be added to the System hive before any increase

in file size becomes apparent.

In the section, “Proactive Avoidance” (page 20), there is a discussion of an HP Management

Service that monitors and alerts Administrators when the System hive is approaching its size

limit. That service leverages existing SNMP- or WBEM-based management infrastructure.

Technical Review 9

Causes of Increasing System Hive Size

When Windows Server 2003 for Itanium-based Systems was first released, the System hive limit

was set to 32 MB by design. This was not changed with the release of Windows Server 2008 for

Itanium-based Systems (although it was increased in Windows Server 2008 R2 for Itanium-based

Systems). At the inception of Windows Server 2003, Microsoft also introduced a new technology

called Multipath I/O (MPIO). This was Microsoft’s strategy for disk multipathing, and included

software that vendors could plug into. As multipathing in storage area networks (SANs) became

more pervasive, the information to be managed (about each disk and path) grew in the System

hive. Up until March 2009, the MPIO framework allowed a maximum of 8 paths per disk. So if

there were 100 disks, then information about 800 different paths had to be stored in each

ControlSet. With the March release of the MPIO framework (Microsoft internal version 1.22,

which the major manufacturers have built their modules on), the maximum number of paths

per disk is now 32, thus quadrupling the space required in each ControlSet for disk information.

Compounding the problem, a popular application often used on Itanium-based scale-up systems

is Symantec’s Veritas Storage Foundation for Windows (SFW). This application is generally used

when large quantities of disks need to be managed. For each disk managed by SFW, an additional

entry is added to the ControlSet.

Another reason for increased System hive size is when there are more than two ControlSets. This

is rare. It only happens when the primary ControlSet failed to load and a “LastKnownGood”

configuration had to be used. When it occurs, the System hive Select key will have a value other

than “0” (zero) in its Failed subkey (refer back to Figure 2). The size of a System hive containing

a failed ControlSet is increased by approximately a third. This can be advantageous however,

since the first two contributing causes listed above tend to increment slowly over time, making

it difficult to determine the cause, whereas a ControlSet failure is much more sudden and easier

to root-cause.

There are other secondary causes for increased System hive size, but they are only manifestations

of the primary causes listed above. Noteworthy of these would be a SAN administrator

inadvertently adding a number of disks to a system incorrectly, and then unpresenting them. In

this situation, Windows maintains a record of these entries since it cannot determine if they are

stale or transient (for example, transient disks would be shared cluster disks), and then adds

them to the ControlSet, never to be removed. A similar situation can occur when a SAN device’s

firmware changes its identity string. Typically the firmware revision, or an incantation of it, is

appended to the Hardware ID subkey. If there are a large number of disks, a firmware update

can be the catalyst that causes a breach of the 32 MB System hive limit.

Breaching the System Hive Limit

As already noted, the System hive limit is hard-coded to 32 MB. This limit cannot be breached.

The file is mapped into system memory with that restriction. This means that whenever a large

addition is made to the system registry, one that takes it to the 32 MB limit, any “overflow” is

lost. In this scenario the registry reaches a point where nothing new can be added, so applications

expecting to add keys cannot function and fail.

Because it is hard-coded, there is no possible way to bypass this system limitation without a

radical redesign of the operating system. In sections, “System Recovery” (page 11), and “Proactive

Avoidance” (page 20), are discussions on how to recover should the server ever breach the limit,

and how to avoid reaching the limit proactively.

Differences in Windows Server 2003, Windows Server 2008, and Windows Server

2008 R2

Windows Server 2003 and Windows Server 2008 for Itanium-based Systems have the same 32

MB limitation for all Service Pack versions. Both operating systems typically collect the same

data in the System hive and are therefore subject to the same root causes of increased hive size.

Windows Server 2008 does have a specific hotfix to alleviate the symptoms, which is described

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