Explanation of LiteSpeed Parameters. (4238535)

LiteSpeed provides a number of different backup options which are set in the LiteSpeed Defaults but may be changed for individual backup and restore jobs.

Some of the options discussed below are advanced options and should only be changed if there is a thorough understanding of the affects the changes.

Affinity

In Windows this is a number which specifies the number of processors that will be used by the running process. Use this to increase performance on multi-processor machines, when operating under heavy loads. Leaving this to 0 (default) provides the best performance in most cases. This is an advanced option, do not alter this setting without referring to the LiteSpeed Help File or SQL Server Books Online by searching for 'affinity' for a complete explanation of the function.

Backup Threads

This is the number of simultaneous processes to use to create the backup. This is used on Multi-Processor environments where the backup job is split over a number of different processes to create the backup file. Large databases tend to be backed up faster when the job load is spread over a number of processes, but as the thread number increases, so does the CPU utilization and IO volume. Each process creates a separate backup file which LiteSpeed interleaves as one backup file. However, if the native files were extracted using the Extractor Utility provided by LiteSpeed, the number of files created is the same as the number set for Threads. These files will need to be restored together, as a set, using SQL Server native restore commands as a striped backup.

Encryption Level

Level of Encryption required. A password will need to be entered to allow the file to be decrypted. There are currently 9 levels of encryption available. The greater the encryption level, the longer it will take to perform the backup/restore.

Compression Level

The level of compression required for the backup. The greater the level of compression the longer it will take to backup/restore a file. The default value is 1 and the max value is 11. A value of 0, bypasses the compression routines; therefore, there is no difference between the Native and LiteSpeed backup file sizes. As the compression level increases, additional time to complete as well as CPU resources may be required.If your server is CPU bound, once processing power is maxed out the performance of the backup will begin to suffer as compression level increases.

Priority

CPU Priority is a setting that adjusts the amount of CPU cycles that the background and foreground applications receive. The default is Normal. Changing this Setting will take up more CPU usage while the backup process is running. Valid options are: 0 Normal (Default), 1 Above Normal , 2 High Note: This parameter is not available for the restore process, only backup

Note:Setting the priority to a higher level should only be done when performance of the backup is more critical than the performance of any other system process (including SQL Server itself).

Max Transfer Size

The maxtransfersize parameter sets the maximum size of each block of data (buffer) that is read into memory prior to compression (the size of the chunks of data that are sent together to the backup device). This parameter can be lowered in order to lessen the memory footprint of a backup if slow performance is being experiencing during the back up process. This should not be set to a value more than 4Mb (4194304 bytes) as this is the limit and it should not be set below 64Kb (65536 bytes). The LiteSpeed default is 1Mb (1048576 bytes).If data is highly compressible, performance may be improved by increasing this value (this is rare though).

Buffer Count
NoteSQLLiteSpeed does not use the buffercount parameter, it simply passes it to the SQL Server. SQL Server uses the buffercount to determine the number of blocks to have ready to give the VDI thread in SQL Server's process space.

Microsoft recommendation the formula below to calculate BufferCount:
NumberofBackupDevices*3 + NumberofBackupDevices + NumberofDatabaseFiles = BufferCount

NoteThe<var>NumberofBackupDevices</var>placeholder is a placeholder for the number of back up devices that you are using to back up the database. The<var>NumberofDatabaseFiles</var>placeholder is a placeholder for the number of database files that you are going to back up. The<var>BufferCount</var>placeholder is a placeholder for theBufferCountparameter.

In LiteSpeed, the maximum value for the buffer count is 150. The buffer count should be set to a number that is greater than the number of backup devices. The LiteSpeed default is 20. This can be changed if performance issues are being experienced with the backup. You can use the BufferCount parameter to change the number of memory blocks that are the size as specified by the MaxTransferSize parameter and that are fetched by the read ahead feature at one instance.

Throttle

The throttle parameter will hard cap LiteSpeed’s CPU utilization at whatever percentage is specified. This parameter refers to overall CPU utilization across all processors. The default is 100%.
Setting the throttle parameter will slow down the LiteSpeed backup, as you are limiting the resources available to the compression engine. If this is acceptable, the throttle parameter is a good option for users performing backups during busy times when they want to make absolutely sure that resources are being left available for database processing. Keep in mind, that by default LiteSpeed will give back resources to SQL Server should they be required by the database, so the throttle parameter typically is not necessary.
Inti Backup Set

The value 0 (default LiteSpeed value) indicates Append backup to backup file set . This is used if an @init value is not supplied.
The value 1 indicates Reinitialize (or overwrite) backup file set.

NOTE: There are also a number of other parameters that can be used, similar to the native backup command, such as STATS=[10%] or SKIP - for the interim refer to the Microsoft web page for full descriptions :http://msdn2.microsoft.com/en-us/library/ms186865.aspx