About direct I/O for backups on Windows
By default, the buffer size for disk storage units is 256 KB. If the buffer size is set to a value greater than 256 KB, backups written to that storage unit automatically use direct I/O. An increased buffer size can improve backup speed.
To increase the buffer size, the following conditions must be met:
A Windows media server must own the storage unit.
The storage unit must be either a BasicDisk or an Array Disk storage unit.
The backup to be stored cannot be multiplexed.
The touch file that disables direct I/O must not be present.
(install_path\VERITAS\NetBackup\bin\DISABLE_DIRECT_IO)
To increase the buffer size, create one of the following touch files on the media server that owns the storage unit:
For backups to disk
install_path\VERITAS\NetBackup\db\config\ SIZE_DATA_BUFFERS_DISK
For backups to disk or tape
install_path\VERITAS\NetBackup\db\config\ SIZE_DATA_BUFFERS
If both touch files are present, SIZE_DATA_BUFFERS_DISK overrides the value in SIZE_DATA_BUFFERS. At this time, Veritas recommends that you use SIZE_DATA_BUFFERS_DISK.
Table: Absolute byte values for SIZE_DATA_BUFFERS_DISK, SIZE_DATA_BUFFERS shows the possible values to include in SIZE_DATA_BUFFERS_DISK or SIZE_DATA_BUFFERS.
Table: Absolute byte values for SIZE_DATA_BUFFERS_DISK, SIZE_DATA_BUFFERS
For a data buffer of this size (kilobytes) | Enter this touch file value |
|---|---|
32 | 32768 |
64 | 65536 |
96 | 98304 |
128 | 131072 |
160 | 163840 |
192 | 196608 |
224 | 229376 |
256 | 262144 |
Data buffer sizes continue in multiples of 32. Multiply the buffer size by 1024 for the touch file value.
A direct I/O backup triggers the following message: "Enabling direct I/O. Buffer size: <buffer size>."
To disable direct I/O
- Create the following touch file on the media server that owns the storage unit:
install_path\VERITAS\NetBackup\bin\DISABLE_DIRECT_IO