Specifications

SCSI to SATA RAID Subsystem | Administrator’s Manual Terminal Operation | en 91
Bosch Security Systems F.01U.027.802 | V1 | 2006.11
7.2 Caching Parameters
7.2.1 Optimization Modes
Mass storage applications can be roughly divided into two categories—database and video/
imaging—according to their read/write characteristics. To optimize system operation, there are
two embedded optimization modes with system behaviors pre-adjusted to different read/
write parameters: “Optimization for Random I/O” and the “Optimization for Sequential I/O.”
Limitations
The following are the limitations on the use of optimization modes.
1. The system default is Optimization for Sequential I/O.
2. You can select the stripe size of each array (logical drive) during the initial configuration.
However, changing stripe size is only recommended for experienced engineers who have
tested the effects of tuning stripe sizes for different applications.
3. The array stripe size can only be changed during the initial configuration process.
4. Carefully consider the outcome before choosing an optimization mode. Once the control-
ler optimization mode is applied, access to different arrays in a RAID system will follow
the same optimized pattern. You can only change the optimization mode after recreating
the arrays.
Database and Transaction-based Applications
These kinds of applications usually include SQL server, Oracle server, Informix, or other data-
base services that keep the size of each transaction down to a minimum, so that I/Os can be
rapidly processed. Due to their transaction-based nature, these applications do not read or
write a bunch of data in a sequential order—access to data occurs randomly. The transaction
size usually ranges from 2K to 4K. Transaction performance is measured in “I/Os per second”
or “IOPS.”
Video Recording/Playback and Imaging Applications
These kinds of applications usually include video playback, video post-production editing, or
applications of a similar nature that tend to read or write large files to and from storage in a
sequential order. The size of each I/O can be 128K, 256K, 512K, or up to 1MB. The efficiency
of these applications is measured in MB per second (MBps).
When an array works with applications such as video or image-oriented applications, the
application reads/writes from the drive as large-block, sequential threads instead of small and
randomly accessed files.
The controller optimization modes have read-ahead buffer and other Read/Write characteris-
tics tuned to obtain the best performance for these two major application categories.
7.2.2 Optimization Mode and Stripe Size
Each controller optimization mode has preset values for the stripe size of arrays created in dif-
ferent RAID levels. If you want a different optimization mode for a configured array, you must
backup or move the stored data and recreate the arrays following the steps below:
1. Stop host I/O access.
2. Move or backup all of your stored data in the subsystem.
3. Change the optimization mode.
4. Reset the subsystem.
5. Recreate the array(s). Once the array(s) are created, stripe size cannot be changed.
Listed below are the default stripe sizes implemented with different optimization modes and
RAID levels. These values should be sufficient for most applications.