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8/13/2019 Backup Compression and Virtual Device Interface
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Backup compression and Virtual Device Interface (VDI)Sunil Agarwal
21 Feb 2010 3:07 PM
People often ask if they can get native SQL Server backup compression using VDI interface. The simple
answer is 'yes' but there are few things you need to be aware of as described below. You can get
details on VDI by clicking link-to-VDI-Specifications.
Within the VDI protocol, the backup application specifies a TSQL backup command. This means that
the backup application can use any TSQL command line options including the option 'WITH
COMPRESSION'. In this case, the SQL Server will send a pre-compressed (using SQL nativecompression algorithm) data stream. However, if the server default is set to always compress, the SQL
Server will not send compressed data stream to VDI initiated backup unless the application specifically
requests it. The reason for this logic is that some backup applications depend on reading and
interpreting the backup stream, and if SQL Server sends compressed bytes, it can potentially break the
backup application. For example, there are 3rd partly backup tools that allow extracting an object (i.e.
a table) from the backup and if the backup is compressed in proprietary format, the tool will not be
able to extract the object. On the other hand, if the backup application explicitly requests the backup
compression, then we know that the application is expecting an opaque, compressed stream.
Secondarily, some backup applications do their own compression and may prefer to use their own
algorithm. Thats perfectly OK too.
Thanks Sunil Agarwal and Kevin Farlee
U VDI protokola, backup aplikacija navodi TSQL backup naredbu. To znai da backup aplikacija moe
koristiti bilo TSQL opcije naredbenog retka, ukljuujui opcije 's kompresijskim'. U ovom sluaju, SQL
Server e poslati unaprijed stlaenih (koristei SQL izvorni kompresije algoritam) data stream. Meutim,
ako je posluitelj zadani je postavljen za uvijek stisnuti, SQL Server nee slati komprimirane podataka
stream na VDI pokrenuo backup, osim akoje zahtjev izriito trai.Razlog za to logika je da su neki
backup aplikacije ovise o itanju i tumaenju backup stream, a ako SQL Server alje komprimirane
bajtova, to potencijalno moe razbiti backup aplikacija. Na primjer, postoje 3rd partly backup alata koji
omoguuju ekstrat objekt (tj. tablice) iz backup i ako backup je stisnut u vlasnikim formatu, alat nee
moi izdvojiti objekt. S druge strane, ako je backup aplikacija izriito trai backup kompresiju, onda
znamo da je primjena oekuje neproziran, komprimiranog stream. Drugo, neki backup aplikacije
napraviti vlastiti kompresije i svibanj elite koristiti svoj vlastiti algoritam. To je savreno u redu previe.