- Sun Storage Virtual Tape Library VTL User Guide

Advantages of VTL tape virtualization
96267 • G Chapter 1 Introduction: VTL appliances and enterprise data-protection 5
Shorterruntimesfornon‐sequentialbackupjobs
Disk‐basedVTLsystemsreduceruntimewhenstorageoperationsarepoorly
matchedtotheoperationalcharacteristicsoftape backupsystems.Properly
configured,streamingtapebackupsachievetransferratesthat areashighasor
higherthanthoseattainable bydisktechnology.Butmanycommo n jobs— suchas
incrementalsandfullbackups
ofworkstations—producesemi ‐random I/ O . Non‐
sequentialI/Okeep stapedrivesbusymounting,unmounting,andpositioning
media,greatlyreducingthroughput.Disk‐based secondarystorageismuchbetter
suitedtothese semi‐randombackupjobs.
Improvedreliability
Disk‐basedVTLsystemscansignific ant ly increasethereliabilityofthebackup
process.Backupjobsaremore lik el ytosucceedthefirsttime,becausethecritical
step—thecreationofacopyofthedata—isasimple ,fastwritetoaRAIDsubsystem.
Jammedtapes,lackofreadymedia,andoff‐line
drivesnolongerruinjobs.See the
figurebelow:
Backup is more reliable with virtual tape libraries
Betterutilizationoftapesubsystems
Disk‐basedVTLsystemscanimproveutilization,performance,andreliabilityof
tape‐storagesubsystems.Whennon‐sequentialI/Oisbackeduptodisk,tapecanbe
reservedforsequentialjobsthatcanstreamaphysicaltapedrive.Large‐scalefull
backupscan,forinstance,godirectlytotape,insuringmaxim umperformance .
Jobs
virtual
library
physical
library
primary storage
A backup to physical tape can fail when a tape
drive jams or media breaks, because a retry may
not be possible before the backup window closes.
physical
library
backup window
FAILURE!
SUCCESS!
A backup to disk-based virtual media always
succeeds, so all data is copied to secondary
media before the backup window closes.
Virtual volumes are
subsequently copied to
physical media outside
the backup window. If
problems arise, copy jobs
can be retried later.