SQL Server Backup – Single or Multi-Threaded Performance?

backupperformancesql server

If you perform a…

BACKUP DATABASE [DB_Name] TO DISK=N'c:\backups\db_name.bak' WITH STATS=10

Will that perform a single or multi-threaded write?

Our Server support company advised us that if we were to multi-thread our backups we would get better disk write performance. They advised us that SQL Backup is multi-threaded, but i think the above statement would be single-threaded. If we specify multiple DISKS to write to, then it will stripe the backup across multiple devices and therefore be multi-threaded by my understanding.

If I perform the following T-SQL while the backup is processing, i can see that the SPID performing the backup has multiple processes, but only one seems to write to disk, the others i presume are reading and doing other things. It's just the write threads i'm referring the question to.

USE MASTER
GO

SELECT *
FROM sys.sysprocesses p
INNER JOIN sys.dm_exec_requests r ON p.spid = r.session_id
WHERE spid=(spid of backup T-SQL)

Thanks in advance.

Best Answer

Backup to multiple files is perhaps what your adviser is referring too. You'll often see improvements (although usually modest) if you're backing up to multiple files on a single disk/array, up to the point that you're saturating source and destination IO paths obviously.

BACKUP DATABASE [MyDatabase] 
TO 
  DISK = N'Z:\backup\MyDatabase_File1.bak'
  , DISK = N'Z:\backup\MyDatabase_File2.bak'
  , DISK = N'Z:\backup\MyDatabase_File3.bak'
  , DISK = N'Z:\backup\MyDatabase_File4.bak'
WITH 
    NAME = N'MyDatabase - Full Backup'
    , INIT
    , STATS = 10

Compression is the obvious addition if you're using 2008+. If not, there are gains to be had from experimenting with BUFFERCOUNT, BLOCKSIZE and MAXTRANSFERSIZE option. Paul Randall's article on Advanced Backup & Restore Options is a good place to start.

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