Sybase 12.4.2 manual Using disk striping, Setting up disk striping on Unix, Balancing I/O, 442

Balancing I/O

Using disk striping

Traditional file management systems allow you to locate individual files on specific disks. Consequently, all file operations occur against a single disk drive. Some operating systems allow you to create logical devices or volumes that span multiple disk drives. Once a file fills the first disk drive, it is automatically continued onto the next drive in the logical volume. This feature increases the maximum file size and concentrates activity on a single disk until it is full.

However, there is another way. Disk striping is a generic method of spreading data from a single file across multiple disk drives. This method allows successive disk blocks to be located on striped disk drives. Striping combines one or more physical disks (or disk partitions) into a single logical disk. Striped disks split I/O transfers across the component physical devices, performing them in parallel. They achieve significant performance gains over single disks.

Disk striping lets you locate blocks on different disks. The first block is located on the first drive. The second block is located on the second drive, and so on. When all the drives have been used, the process cycles back and uses additional blocks on the drives. The net effect of disk striping is the random distribution of data across multiple disk drives. Random operations against files stored on striped disks tend to keep all of the drives in the striped set equally busy, thereby maximizing the total number of disk operations per second. This is a very effective technique in a database environment.

You can use disk striping either as provided by your operating system and hardware, or IQ’s internal disk striping.

Setting up disk striping on UNIX

UNIX systems offering striped disks provide utilities for configuring physical disks into striped devices. See your UNIX system documentation for details.

Setting up disk striping on Windows NT

On Windows NT systems, use hardware disk striping via an appropriate SCSI-2 disk controller. If your machine does not support hardware disk striping, but you have multiple disks available for your databases, you can use Windows NT striping to spread disk I/O across multiple disks. Set up Windows NT striping using the NT Disk Administrator.

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