The book started with the ‘Foreword’ page consists of ‘History of ASM’ headline which is written by Bill Bridge (an architect in Oracle over 18 yrs and the creator of ASM).
He revealed few interesting points about ASM history, like when did he get an Idea about ASM, how it can be useful with Oracle technology and the total time which took to build ASM technology.
Chapter 1 – Storage Stack Overview
This chapter starts explaining an overview about Disk drive technology, disk layouts, Disk Drive performance, different class of storage system architectures (such as SAN, NAS, DAS and SCSI) .
RAID levels also been discussed, and storage arrays concepts too.
Conclusion:
It might look interesting, but, I have skipped this chapter in order to read more about ASM concepts.
Chapter 2 – ASM Instances
This chapter starts on a note about ASM introduction, managing ASM (startup/shutdown) instances, few important ASM Instance parameters (such as instance_type, asm_diskstring & asm_diskgroups), ASM instance new background processes, V$ ASM views, ASM installation, upgrade and patching concepts.
It also talk about the significance of two ASM files, the ‘ab_
These files are used by the RDBMS instances for env. Information and health check monitoring.
Note : Beware, these files should not be deleted.
Conclusion:
Nothing new has been offered in this chapter. This information is already available in the Oracle documents.
Chapter 3 – ASM disk
This chapter starts explaining about logical term LUN and explained about creating LUNs, LUN optimal sizes and what is the minimum disk size (4mb) and maximum (2 power 32 MB). Also, explained disks discovery(asm_disktring init parameter) and explained the meaning of disk header status (Former, Candidate, Member & Provisioned).
It also talks about the disk preparation/configuration on different OS, such as, Solaris, AIX and Windows and how to use the asmtool & asmtoolg utilities.
Conclusion:
Nothing new offered in this chapter as well.
Chapter 4 – Diskgroups and Failure Groups.
This chapter started explaining about ASM diskgroup concepts and why ASM diskgroups are differ from typical LVM (logical volume manager). Also discussed ASM diskgroups redundancy types (normal, high and external) and their practice.
In the next segment of this chapter, it talk about Creating Diskgroups, default ASM Disk Names & how to change default disk naming convention and Diskgroup Numbers. An interesting point was made, i.e., “you are not restricted to having two failure groups for normal redundancy and three for high redundancy”.
Couple of new feature of v11g ASM, ASM Preferred Read, Diskgroups Attributes and Fast Disk Resync have been discussed.
In the last segment of this chapter, it explained I/O concepts and I/O failures. The chapter finished explaining about the Space Management Views and important columns that need to consult for space management.
Conclusion:
This chapter gave some good inputs about I/O errors, 11g new features, ASM extent management , understanding of redundancy level and etc.
Chapter 5 – ASM Space Allocation and Rebalance
I particularly liked this chapter, it presented deeper insights about ASM Space allocation, operations, such as ASM AU (Allocation Units), ASM Extents distribution evenly among existing disks, how ASM Strips works, and difference between coarse and fine-grained striping types and which type of striping is good for what type of database files.
It also discussed when to change the default values of _asm_ausize (deault 1m) & _asm_stripesize (128k/1M) and how to set/change values for VLDs databases.
I also like the way author explained about ASM Rebalance operation concepts and the impact of setting various values to the ASM_POWER_LIMIT init parameters.
I really like the point “It is commonly believed that adding and dropping a disk against the same diskgroup required two separate rebalance activities. In fact, disks can be dropped and then added and a single rebalance command can be evenly distribute the I/O”. It shows how to avoid two rebalancing operations on this occasion.
A 11g new feature Fast Rebalancing which overhead of ASM-to-ASM and ASM-toRDBMS messaging also been discussed.
Conclusion:
I really enjoyed reading this chapter which gave me great insight of ASM extent mechanism, rebalancing and striping internals. It also provides few very useful scripts.
Chapter 6 – ASMLIB Concepts and Overview:
Since I have not worked much on Linux, I have quickly reviewed this chapter about ASMLIB API which is currently available on Linux OS.
This chapter explains the benefits of ASMLIB API, and the following functionality of ASMLIB:
Device Discovery I/O processing Performance and reliability
Explained ASMLIB configuring, Managing disk in ASMLIB, Upgrading ASMLIB, Migrating to ASMLIB and troubleshooting ASMLIB.
Chapter 7 – ASM Files, Alias and Templates
This chapter explains about the default ASM Filenames, creating tablespaces, ASM Alias and Templates.
Conclusion:
Nothing new offer in this chapter.
Chapter 8 – ASM Command-Line
This chapter explained about the ASMCMD (unix based) utility and its usage. It starts explaining existing means to manage and access ASM and its components.
I really liked the following 11g new features:
Bad Block Remapping in ASMCMD. Starting with 11g, when ASM redundancy is used, it is possible to recover bad sot by restoring the data from their mirror copy using the ‘remap’ command.
Note : ‘remap’ don’t fix logical errors or corruptions detected by the RDBMS.
ASMCMD Copy:
Starting with 11g, moving datafiles in and out of ASM made easy with “copy” command introduced in ASM.
Conclusion:
11g couple of new features about ASMCMD utility worth to know.
Chapter 9 – Managing Databases in ASM
This chapter started on a note on how to use ASM while creating databases and covered some good points about the internal functionality of CSS (Cluster Synchronize Services) daemon/process, how RDBMS interacts with ASM, important background process (role of RBAL, ASMB & 00nn b/g), few vital parameters that influence ASM performance (like, processes + add 16, large_pool add additional 60k and shared_pool size additional memory to store extent maps and concluded with good examples of converting ASM no non-ASM and vice-versa.
Conclusion:
Explained well about CSS internal behavior, how RDBMS communicates with ASM instance, converting instances from ASM-to-Non ASM and vice versa.
Chapter 10 – ASM Persistent Data Structures
Stars explaining about MEATADATA and where does ASM stores the metadata, and different types of metadata. ASM has two main classes of metadata, physical and virtual metadata.
Physical metadata which located at fixed locations on disk contains the following:
Disk Header Allocation Table(AT) Free Space Table (FST) Partnership Status Table (PST)
Virtual Metadata stored in ASM files and contains the following:
File Directory Disk Directory Active Change Directory (ACD) Continuing Operations Directory (COD) Template Directory Alias Directory Attribute Directory Staleness Directory Staleness Registry
Chapter 11 – ASM Operations
This chapter is one of those chapters I liked in this book. It really explains how ASM works internally on the following condition:
First time when RDBMS instance tries to access an ASM file. Operations on ASM Files File creation File open File input/output (I/O) File close File delete
It also talk about the variable sized extents and Striping types (such as Coarse and fine-grind), Resync, Rebalancing and ASM Instance Recovery & Crash Recovery concepts.
Conclusion:
This is one of interesting chapters present in this book which offers an internal mechanism of ASM functionality on the above mentioned operations.
On APPENDIX
Appendix A: explained about ASM and Storage Array Configurations.
Appendix B : Troubleshooting – In page, it discussed about ASM startup issues, Diskgroup mounting issues, Space related Issues and a walkthrough of an ASM alert log.
Appendix C: Scripts and Tips - Automatically Starting up and Shutting down ASM instance in Non-RAC env.
Migrating Individual Non-ASM datafiles to ASM.
Overall thoughts:
This book is recommended for someone who serious wants to study about ASM technology and its in & outs.
Having a copy of this book is better than scanning 100th of Oracle documents.
This book is summarized and explained all ASM contents to a great extent.
For me, I liked 4 chapters in this books and might need another read.
Happy Reading
Jaffar
