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Knowledge Base

Improving backup performance via tuning Netbackup buffer size

Publication Date:  2015-09-07  |   Views:  8385  |   Downloads:  0  |   Author:  i00325014  |   Document ID:  EKB1000085735


Issue Description

Issue Description

While using Huawei OceanStor VTL6900 and Netbackup (for Windows) in your backup environment (backups to VTL over SAN) you may face with unexpectedly low backup performance. Important notice that at the same time backup to disk array (for example to storage, not VTL) may perform up to several times faster speeds in exactly the same software and hardware conditions and network topology.


By default Netbackup data buffer size value is 65536 bytes for backup to tape and 262144 bytes for backup to disk. Because of Netbackup recognize Huawei VTL as common tape library, the default value buffer size for tapes is used by Netbackup (65536 bytes), while actual backups are stored on disks. That can significantly reduce backup performance.


In order to increase backup performance of backup to VTL, buffer size should be increased. To increase the SIZE_DATA_BUFFERS setting, on Windows Media Server host create a file called SIZE_DATA_BUFFERS in the <INSTALL_PATH>\NetBackup\db\config\.  Add the desired value in this file, expressed in bytes, in multiples of 1024. Ensure the file has no extensions after saving.  If the file is not present, the default for the SIZE_DATA_BUFFER is 65536.

However, most real practical cases show that value of 262144 bytes is best fit for most types of environment, testing different values is strongly suggested.

NOTICE 1: This solution has to be applied on NBU Windows Media Server.

NOTICE 2: Be careful when changing the value from the default setting as some SCSI cards, HBA cards, and tape drives cannot transfer buffers greater than 65536 in size efficiently and correctly.  After changing this value, it is important to test both backups and restores, as sometimes data can be written at the modified size, but cannot be read at the modified size.   Please review the specifications of the HBA card, SCSI card and tape drive to confirm that the vendor recommended values are not being exceeded.