Sun Microsystems Virtual Tape Library Uživatelský manuál stáhnout pdf (Strana 21)

Advantages of VTL tape virtualization

96267 • G Chapter 1 Introduction: VTL appliances and enterprise data-protection 7

Operatingsystemsandbackupapplicationsthatcurrentlyinteractwithaphysical

libraryviaACSLScontinuetouseACSLSwhenaccessingVTLvirtuallibraries.

ACSLSfurt he rhidestheparticularsofdisk‐basedtapevirtualizationbehinda

standard,well‐knowninterface.

Thisabilitytomaskthelibrar yimpl emen tat ionfromclientapplicationsand

operating

systemsletsACSLSmakedisk‐basedtape‐virtualizationavailableto

platformsthatcouldnototherwise supportit.Platformsthatdonotsup portSCSI

passthroughlibrarycontrol,suchasUni sy s, Tangent,andmainframeoperating

systems,canbackuptoSunVTLvirtu a llibrariesusingACSLS.

Themorepowerful,more specializedli brary‐

controlfunctionalityof ACS LS 

improvestheavailabilityofsuitablyconfiguredVTLsolutions.ThebriefSCSIpath

interruptions that mayaccompanyfailoverandfailbackarelesslik el ytointerfere

withthebackupapplication,because ACS LS retriestheconnectiona gg res sively

enoughtorestorethepath.

Truetapevirtualizationwithdynamically

allocateddiskspace

Correctlyconfigured,dynamicallysizedvirtualtapevolumesprovidethehighest

capacityandperformance.WhentapesarecreatedwiththeVTLCapacityOn

Demandfeature enabled,theVTLsoftwareallocatesspaceasdataiswrittentodisk

ratherthanallatonce.Forinstance,aphysicaltapewithacapacityof400

‐GBcan be

emulatedwithoutallocatinganyspaceinitially,andthereafterenlargedas neededin

5‐GBinc reme nts (seethefigurebelow).

Thisapproachtospaceallocationhastwomajor ad vantages.First ,itminimizes

wasteddiskcapacity.Second,andperhapsmoreimportantly,itmaximizesarray

performanceandrelia bil it y.Dividingdata

intomult ip le segmentsdistributesitmore

evenlyacrossthearray,involvesmorevolumegroupsineachI/O,andreducesthe

averagelengthofeachseek duringI/O.

Space is not allocated on

disk until data is written

400-GB physical tape 01A00001

400-GB physical tape 01A00002

400-GB virtual tape 02B10001

= 5-GB header/data segment = 5-GB data segment

= 2-MB tape archive files

400-GB virtual tape 02B10000

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Sun Microsystems Virtual Tape Library Uživatelský manuál Strana 21