Intel RAID Controllers Interoperability Guide

Setup Array using an Intel® RAID Controller DIY Storage System Guidance Using Intel® Server RAID Controllers Deployment Practices White Paper

Revision 1.0

The following table provides a quick reference for RAID settings. This information is simplified

and may not be accurate with some applications or tests. For detailed performance tuning

information, refer to the Intel

RAID Controller Performance Optimization White Paper available

at http://support.intel.com/support/motherboards/server/

Table 8. RAID Settings

I/O Policy

Direct I/O

Read Policy

Adaptive Read Ahead

Write Policy

Write Back*

* A RAID controller battery should be used whenever virtual drive write-back cache is enabled and data is mission

critical.

5.1.4 Hard Disk Cache

Disk drive cache can be enabled in the Virtual Drive Properties page of the RAID configuration

utility. There is a risk of data loss using a hard drive cache; an overview is provided below.

Hard disk drive cache is located within the logic of the hard drive. Cache provides enhanced

performance for sequential read access by retrieving adjacent data on the drive into the data

buffer in case the host computer requests it. This process allows the data to be directly

transferred from the drive’s memory when it is requested rather than waiting for a disk access,

which results in lower latency. Enabling the hard drive cache can also improve write

performance by providing additional memory space for queued data. Write data can be queued

in the disk cache and reported as written even though the data will not move from memory to

the disk until disk access is available. This reduces the delay during disk I/O operations.

There is an inherent risk in holding data in the drive cache when a write has been

acknowledged as complete but is not written to the disk. If the drive loses power, the data in the

cache is lost before it is written to the disk. This can cause a “hole” in a data file, which makes

the file unusable. Using a UPS mitigates this risk but does not eliminate it.

Note: A soft or hard reset (<Ctrl> + <Alt> + <Del> or the reset button) does not affect the

completion of a disk write operation because the disk cache is flushed as long as drive power is

maintained.

5.2 RAID Configration Demo for Applications

To set up a surveillance server, make sure that your storage system can provide large capacity

for video data storage, and with optimized performance. To keep the video safe, store the

application data (video data) separate from the operating system so that the application data is

not impacted in case the operating system needs to be reinstalled.

To meet this requirement, create RAID 1 using 2 HDDs to only install the operation system

without the application data. Then, create RAID 50 using 12 HDDs to create a large capacity for

data storage to contain the surveillance application and data. The remaining hard drives can be

used as online hot spares to help recover a failed drive utilizing the auto rebuild feature of the

RAID controller.