Oracle 10g Automatic Storage Management

Oracle 10g Automatic Storage Management, Part 1: OverviewBy Jim CzuprynsiSynopsis! Oracle 10g's new Automatic Storage Management (ASM) features allow an Oracle DBA to take advantage of a robust fle!ible scalable file storage s"stem t#at an" Oracle database instance can access$ %#is article & t#e first in t#is series && 'rovides a #ig#&level overview of t#e ASM arc#itecture and s#ould be #el'ful to an" DBA contem'lating t#eado'tion of ASM for storing Oracle database files as 'art of a #ig#&volume storage solution$With the possible exception of having to rebuild a database server from a "cold metal" starting point, I have to admit that the scenario that holds the most dread for me as an Oracle DBA is to run out of disk space for a production database's datafiles or tempfiles !hough, in most cases this situation can be rectified easil" # as long as there is sufficient disk space available, of course$ # it al%a"s seems that these challenges seem to occur eitherat the busiest time of m" client's business da", or bet%een &'(&& and &)(&& on an earl" *unda" morning %hen I am scheduled to be out of to%n en+o"ing a long %eekend And I have also encountered m" share of unexpected ,and unlikel"- disk media failures .or example, I once %atched five disks in a /'#disk mirrored storage arra" fail %ithin a three#%eek period after three "ears of relativel" solid performance !he pattern never repeated itself, but it did teach me the value of a good mirroring strateg"$While a storage area net%ork ,*A0- and other logical volume manager ,123- storage solutions like 435 are certainl" options for guaranteed storage reliabilit", the costs of these solutions can be prohibitive for smaller I! organi6ations !he good ne%s is that Oracle 7&g supplies a ne% set of disk media storage features called Automatic Storage Management (ASM) that are aimed directl" at insuring a storage solution for smaller enterprise databases !his series of articles %ill delve into A*3's rich features and provide examples of ho% to implement some simple A*3 disk configurations for evaluation purposes so that "ourDBA team can make some decisions about %hether A*3 is %orth pursuing for "our organi6ation I %ill concentrate this article on a general revie% of A*3 features as %ell as a brief explanation of the A*3 architectureAutomatic Storage Management "eaturesOut#O$#%&e#Bo' "unctionality! .irst off, A*3 %as designed s'ecificall" for t#e storage of Oracle database files !his means that it is read" "out of the box" for use against an" Oracledatabase that it services !hough A*3 appears to be the intended replacement for Oracle 5luster .ile *"stem ,O5.*- for the 8eal Applications 5luster ,8A5- environment, that doesn't mean that "our database needs to be deplo"ed under 8A5 to take advantage of A*3's m"riad features9 A*3 can be deplo"ed on a single 'rocessor (SM() server +ust as easil" as it can be deplo"ed on a multiple#node 8A5 cluster$ 3oreover, it is simple to configure using the graphic interface provided b" the Database 5onfiguration Assistant ,DB5A-, an existing Oracle tool that +ust about ever" Oracle DBA has used Oracle 7&g also provides the standard 4nterprise 3anager ,43- interface for managing an A*3 instance once it has been created"le'i(le Storage Con$iguration! *ince A*3 is in essence its o%n file management s"stem, this means that I can add more '#"sical storage c#ange storage configurations or remove e!traneous storage %ithout having to shut do%n m" Oracle database to change out ph"sical hard%are !his is a big advantage over traditional hard%are configurations, and is certainl" featured in storage#area net%orks ,*A0s- :sing A*3 also means that I can turn over the ma+orit" of m" space management tasks to the A*3 instance and let it monitor the gro%th of m" database's tablespaces In addition, A*3 maintains pre#existing Oracle database functionalit", so regular Oracle databases can continue to operate as usual 0e% database files can be created as A*3 files managed b" the A*3 instance, existing database files can be migrated to A*3 as time and opportunit" permit, and other database files can continue to exist as "traditional" database files %ithout A*3 file management"ault %olerance! I also expect an" file management s"stem to insure that once I %rite database information to disk, it %ill never be lost # unless, of course, I tell the database to delete that data One %a" that DBAs usuall" guarantee against the inevitable failure of disk hard%are is through mirroring drives via redundant arra"s of inexpensive disks ,aka 8AID- and stri'ing ,%riting portions of disk files to different disks so that if one disk is lost the information is recoverable from another disk in the set- !his guards against the inevitable failure of disk hard%are, since even %ith extremel" high estimated mean time bet%een failures ,3!B.-, a disk drive %ill almost certainl" fail eventuall"3ost operating s"stems provide controls to set up and monitor disk storage to take advantage of these redundanc" features 1ike an" good file management s"stem, A*3 provides fault tolerance b" allo%ing me to %rite duplicate or triplicate copies of an" database files' contents And if m" current server and disk storage s"stem alread" support fault tolerance, so much the better$ A*3 can also take advantage of e!isting vendor&su''lied fault tolerance mec#anisms for increased guarantees to safe data storage*ince A*3 handles the mirroring of data, there is no need to purchase a third#part" 1ogical 2olume 3anager ,123- 3irroring is applied on a file&b"&file basis, rather than on a 'er&volume basis, so the same disk group ma" contain a combination of files protected b" mirroring ,or perhaps not even mirrored at all, if mirroring is not re;uired for some files- A*3 also supports Oracle 8eal Application 5lusters ,8A5- so there is no need for a separate5luster 123 or a 5luster .ile *"stem)*O +oa, Balancing! A*3 is responsible for providing e;ual distribution of )*O loads across all available disk storage resources, so there is a measurable performance improvement .or example, A*3 %ill split a datafile into its component extents and then spread those extents evenl" across all defined disks that A*3 is managing9 those extents are then tracked via an indexing techni;ue A*3 also automaticall" manages data via selection of desired reliabilit" and performance characteristics instead of manuall" manipulating data file storage characteristics, and therefore it tends to reduce ,or even eliminate- manual tuning and retuning of I1E startup mount9A*3 instance started!otal *"stem Alobal Area7&&LL)'PL b"tes.ixed *i6e ONOL/N b"tes2ariable *i6ePPNOML/N b"tesDatabase Buffers& b"tes8edo Buffers& b"tesA*3 diskgroups mountedS&utting /own an Active ASM )nstance! !o shut do%n this A*3 instance, I once again set the O-AC+0BS)/ environment variable and then simpl" issue the S4.%/O>2 )MM0/)A%09 command(KE export O8A514G*IDFHA*3KE s;lplus "s"s as s"sdba"*>1E 5onnected*>1E shutdo%n immediate9A*3 diskgroups dismountedA*3 instance shutdo%n*>1E)mplications o$ S&utting /own an Active ASM )nstance! 0o%, a %arning( When an A*3 instance is shut do%n, it is important to be a%are of the implications for an" regular Oracle database instance that is using A*3 files stored on that A*3 instance !he A*3 files %ill not be accessible to those regular Oracle databases until the A*3 instance is restarted/emonstrating ASM in a Sample /ata(ase0o% that I have explained ho% to create, start, and stop an A*3 instance, I %ill next demonstrate ho% to add a tablespace to an existing Oracle database instance that uses the A*3 instance's disk group instead of the database instance's disk storage to store the ne% tablespace's datafileCreating an ASM#Manage, %a(lespace! What I reall" like about A*3 is its simplicit" I no longer need to be concerned if the tablespace's datafile %ill fit on the drive or spindle I have targeted for storage9 I simpl" inform A*3 that it is responsible for storing the datafile and ho% large the datafile is, and A*3 handles the rest All I needed to do to create a ne% tablespace, %BSBASM1, %as to issue the follo%ing C-0A%0 %AB+0SPAC0 command from a *>1I@lus session running against the database instance(*>1E 584A!4 !AB14*@A54 tbsGasm7 DA!A.I14 'HDA8O:@7' *IQ4 )'39!ablespace created0ote that I did not have to specif" the exact location of the datafile, since A*3 determined from the si6e of the tablespace exactl" ho% it should be striped across the disks in the A*3 disk group 3oreover, since A*3 uses Oracle 3anaged .iles ,O3.- for naming the datafile, A*3 automaticall" named the datafile using the appropriate O3. standard ,I %ill delve into A*3 file naming conventions in greater detail in the next article in this series-4ven more interesting, I did not have to do an"thing special to inform the database instancethat it needed to start up the appropriate 8ebalancing ,8BA1- and A*3 Bridge ,A*3- processes As soon as this ne% tablespace %as created, the database instance detected thatA*3 storage %as in use, and it automaticall" started these t%o background processes, as this snippet from the database's alert log clearl" sho%s(

*un Dec 77 7N()M(&& '&&M584A!4 !AB14*@A54 tbsGasm7 DA!A.I14 'HDA8O:@7' *IQ4 )'3*un Dec 77 7N()M(&) '&&M*tarting background process A*3BA*3B started %ith pidF'7, O* idFOOL*tarting background process 8BA18BA1 started %ith pidF'', O* idF)M'/*un Dec 77 7N()M(&P '&&M*:554**( diskgroup DA8O:@7 %as mounted5ompleted( 584A!4 !AB14*@A54 tbsGasm7 DA!A.I14 'HDA8O:@7' *IQ

Migrating an 0'isting %a(lespace to ASM#Manage, Storage! Another great thing about A*3( I did not have to recreate an existing tablespace %hen I %anted to migrate it to A*3 storage Instead, I used 8ecover" 3anager ,83A0- to create an image co'" of the tablespace's datafile, and then I simpl" migrated that datafile to A*3 !o demonstrate, I created a ne% tablespace in the database instance I then issued the appropriate 83A0 commands to take the tablespace offline, create the image cop" of the tablespace, transfer the tablespace to A*3, and then bring the tablespace back online *ee +isting =!; for the *>1 statements and 83A0 commands that I used to complete this taskSetting .p 0nterprise Manager 50M6 $or ASM )nstance ManagementOracle 7&g 4nterprise 3anager ,43- does provide a simple and elegant %a" to manage A*3storage9 ho%ever, I needed to reconfigure m" database instance's 43 configuration to take advantage of these tools via the 4nterprise 3anager 5onfiguration Assistant ,435A- Once I had created the A*3 instance and had then created at least one A*3#managed file in m" database instance, I removed the original 43 configuration for the database instance and then replaced it %ith a ne% 43 configuration that full" supports A*3 A sample set of 435A commands are sho%n in +isting =!