- Sun Storage Virtual Tape Library VTL User Guide

Managing virtual libraries
96267 • G Chapter 4 VTL operations 45
Nexttask:
■ Ifyouaregoingtoconfig uretapecachingon thisvirtuallibrary,goto
“Configuring AutomatedTapeCaching”onpage 45.
■ Ifyouaregoingtousetheautomaticarchivingfeatur es,goto“Settingupthe
AutoArchivefeature”onpage 49.
■ Ifyouaregoingtousetheautomaticreplication feature, goto“Settingupthe
AutoReplicationoption”onpage 50
■ Otherwise,goto“Generatingthevirtuallibrary”onpage 51.
ConfiguringAutomatedTapeCaching
YouconfigureAutomatedTapeCachingforthevirtuallibraryby defininga
migrationpolicyand areclamationpolicy.AVTLpolicyissimplyasetofcriteria
(triggers)thatcontrolhowandwhenVTLsoftwareautomaticallymovesdatafrom
itsphysic al diskcache.Usingtheconfigurationdialogs,you ca n 
specifysimple
schedulesormorecomplexstate‐andevent‐drivenpolicies.
MigrationpoliciescontrolwhenVTLcopiesdatafromthediskcachetophysi cal 
tape.Goodmigrationpoliciesmaximizetheperformanceandreliabilityofthedisk
cachebyminimizingsimultaneousreadsandwrites.Simultaneousread s and 
writes—crossI/O—forcediskarraysto
switchbackandforthbetweenmultiple,
competingI/Oste am s,reducingthroughputandsubjectinghardwaretoexcessive
wear.Sobestpracticeistoschedulemigr ationassoonaspossibleafterabackup
ANDatatimewhenotherbackupjobsarenotrunning.
Reclamationpolice scontrolwhenVTLreleasesthediskspace
thatis usedbyadata
setthathasalreadymigratedtotape.Promptandefficientreclamationprevents
over‐subscriptionofthediskandconsequentbackupfailuresandsystemdowntime,
whileminimizinginvestmentincachecapac ity.Bestpracticeistoreclaimspaceas
soonasthehighest demandfor
restoreshaspassed—typicallyafterthreetofive
days.Thisapproachstrikesthebest balancebetweentakingadvantageofthespeed
andconvenienceofadisk‐basedrestoreandminimizingconsumptionof cache
space.
Tocreateamigrationpolicy,selectoneofthefollowingapproaches:
■ “Creatingsimp le schedule‐drivenmigrationpolici es” onpage 46
■ “Creatingstate ‐andevent‐basedmigrationpolicies”onpage 4 6.
Thengoto“Creatingareclamationpolicy”onpage 48.