Day 12 of 31 Days of SQL Server Backup and Restore using PowerShell: Simple Transaction Restore

Yesterday we looked at simplest possible example of a SQL Server restore; restoring a single backup file. Now we’re going to get a little bit smarter, and also restore transaction logs.

So the scenario is that you have folder containing your full database backup and the subsequent transaction logs, like so:

PS C:\> gci c:\psbackups

    Directory: C:\psbackups

Mode                LastWriteTime     Length Name
----                -------------     ------ ----
-a---        13/09/2013     11:23    2648576 psbd1_backup_201309131100.bak
-a---        13/09/2013     11:23    1800704 psbd1_backup_201309131105.trn
-a---        13/09/2013     11:23      90624 psbd1_backup_201309131110.trn
-a---        13/09/2013     11:23      90624 psbd1_backup_201309131115.trn

PS C:\>

So how do we do this? Well, exactly how we’d do it in T-SQL. Restore the Full backup with NoRecovery and then restore all the transaction log backups in order, also with no recovery, and then recover the database after the last one on has been restored.

Normally that means writing lots of lines of T-SQL (it’s always just before the next full backup isn’t it, and you have 92 transaction logs to restore!). Thanks to PowerShell’s objects we can do better than than.

So to the script:

Import-Module SQLPS -DisableNameChecking

$SQLSvr = New-Object -TypeName  Microsoft.SQLServer.Management.Smo.Server -ArgumentList ("Server1")
$Restore = New-Object -TypeName Microsoft.SQLServer.Management.Smo.Restore
$DeviceType =[Microsoft.SqlServer.Management.Smo.DeviceType]::File

$Restore.Database='psrestore'
$Restore.NoRecovery = $TRUE

$Files = Get-ChildItem C:\psbackups\
$i=1

foreach ($File in $Files){
	if($i -eq $Files.count){
	    $Restore.NoRecovery= $FALSE
	}
	$BackupDevice = New-Object Microsoft.SqlServer.Management.Smo.BackupDeviceItem -ArgumentList $file.FullName, $DeviceType
	$Restore.Devices.Add($BackupDevice)
	$Restore.SQLRestore($SQLSvr)
	$Restore.Devices.Remove($BackupDevice)
	remove-variable BackupDevice
	$i++
}

First we do our normal setup, loading the SMO module and creating some basic objects. Next we set the name of the database we’re restoring, and also tell our $Restore object that we don’t want to recover the database at the end of the Restore (the default option is to recover them).

We use the Get-ChildItem cmdlet to load the contents of our backup directory into an object called $Files, and create a counter variable $i and initialise it to 1.

We now step through each $File in our $Files object. We use the $Files.count property and $i to work out when we are restoring the last file in the list, and when we are we set $Restore.NoRecovery to $FALSE, thereby recovering the database after the restore.

We restore the file and increment the counter variable by 1, and then go through the loop again if we aren’t on the last file.

We can do the same with the Restore-SQLDatabase cmdlet introduced with SQL Server 2012

Import-Module SQLPS -DisableNameChecking

$ServerName = "Server1"

$RestoreDatabase='psrestore'
$Files = Get-ChildItem C:\psbackups\
$i=1

foreach ($File in $Files){
    Restore-SqlDatabase -ServerInstance  $ServerName -Database $RestoreDatabase -BackupFile $File.FullName -NoRecovery

    if($i -eq $Files.count){
    Restore-SqlDatabase -ServerInstance  $ServerName -Database $RestoreDatabase -BackupFile $File.FullName
    }
    $i++
}

When we use this cmdlet we can’t set the NoRecovery property as we did with SMO, as it’s not a parameter but a switch. So we us the same logic to find when we’re restoring the last file, and then run the cmdlet again without the -NoRecovery switch.

This fairly straightforward, and simple to write it you know that you only have the files for 1 database in a folder, and they’re in correct chronological/LSN order with the full backup being the oldest. But what do you do if you just have a folder full of random files from multiple databases from multiple days with a mix of full, differential and transaction backups? Well, that’s what we’re going to explore over the next couple of days. Tomorrow we’ll begin by looking at how to look inside the backup files.

This post is part of a series posted between 1st September 2013 and 3rd October 2013, an index for the series is available here.

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