Adaptive Server allows you to create and mount database devices
on raw bound devices for raw disk IO. Raw disk IO has performance
advantages since it enables direct memory access from user address
space to the physical sectors on the disk, omitting needless memory
copy operations from the user address space to the kernel buffers.
Raw disk IO also assumes that logical and physical IO are
simultaneous, and writes are guaranteed to flush to the disk when
the system write() call returns.
When
preparing a raw partition device, follow these guidelines:
-
Do not initialize
a database device on the partition that contains your Sybase installation
software. Doing so destroys all existing files on that partition.
-
A raw partition designated for use by Sybase cannot
be mounted for use by the operating system for any other purpose,
such as for file systems or swap space.
-
After
a Sybase configuration utility or the disk init command
has initialized a portion of a partition as a database device, the
entire partition cannot be used for any other purpose. Any space
left on the partition beyond the size specified for the device can
be reused with the disk resize command.
-
To avoid any possibility
of using a partition that contains the partition map, do not use
cylinder 0.
-
Place
the database device on a character device, because the Adaptive Server
recovery system needs unbuffered system IO.
-
To determine whether a device is a block device or a character
device run:
ls -l <device path>