So you’re now at the point in your business that you need to purchase a server to host your applications, files and printers. Or maybe you are in the market for a server so you can control security on your network more effectively. Either way, there are two important factors that you must understand besides the speed of the server and the hard drive capacity. This is your raid controllers and the difference between SATA and SAS hard drives.

Software Raid vs. Hardware Raid Controllers

A Software raid controller is dependent on the operating systems CPU performance and load. This is not much of a factor, because of today’s faster CPU’s and in some instances a software raid can outperform a hardware raid. This is obviously dependent on the CPU that is selected at the time of the server purchase.

Recovering from a software raid controller failure in our experience has been more difficult because of the lack of raid logs. Hardware raid controllers have provided us with a more in-depth cause of the failure, leading us to a better action plan for recovery. Whether a software raid or hardware raid is selected it is always important to have a proven tested backup.

Cost – Software controllers are less expensive, because it is built into the server OS. The only other cost that you would have in a software raid environment is the cost of the hard drives.

Vulnerabilities – Because software raid is a running application at the software level it can be impacted and become vulnerable to viruses which could impact the raid functionality. Another key factor to a software raid implementation is that, in some cases if your server fails to boot because of a corrupted OS this can affect your raid resulting in data loss.

Performance – Depending on which raid level is selected for your sever build, there are pros and cons to both software and hardware raid controllers. In this instance let’s take a raid level 5 (raid 5 is not for performance. Raid 5 is a fault tolerant raid level). As we discussed, a software raid controller is dependent of the server OS and CPU, if you have high activity on your server, this will reduce your servers’ performance. A hardware raid controller on the other hand, will take the load of the servers’ activity and then distribute the activity to your selected hard drives. Some people may say that the performance increase over a hardware raid controller is negligible.

SAS vs. SATA

The following information has been “clipped” from Intel’s website. You will find that the below chart explains in detail the operational differences between SAS and SATA hard drives.

Requirement

 

SAS

 

SATA

 

Operational Availability

24 hours/day – 7days/week

8 hours/day – 5days/week

Workload

100%

10-20%

Cost Sensitivity

Moderately sensitive to cost

Sensitive to low cost

Performance

Latency and Seek

5.7 msec @ 15K rpm

13 msec @ 7200rpm (or smaller)

Command Queuing and Reordering

Full

Limited

Rotational Vibration Tolerance

Up to 21 rads/sec/sec

Up to 5 to 12 rads/sec/sec

Typical I/Os per sec/drive

319

77

Duplex Operation

Full

Half

Reliability

Bad Sector Recovery

Typical time out 7-15 sec only

Time outs up to 30 sec

Misalignment detection

Dedicated Servo and data path processors

Single combined servo/data path processor or none

Vibration Sensors

RV Compensation Feedback Mechanism

No RV Compensation

Variable Sector Size

Utilizes a 528 byte sector and allow the I/O controller

Do not utilize a variable sector size (locked at 512 bytes)

MTBF

1.2M hours at 45 degrees C

700K hours at 25 degrees C

Internal Data Integrity Checks

End to End

Limited, none in memory buffer

Maximum Operating Temperature

~60 degrees C

~40 degrees C

Warranty

~5 years

~ to 3 years

Features

Spindle Motor

Higher RPM
Tighter run-out
Spindle anchor at both ends

Moderate to lower RPM
Lower specification for run-out
Spindle anchored at one end

Media

Full media cert

Lower media specification and density

Head Stack Assembly

Structural rigidity
Lower inertial design

Lighter Weight Design
Higher inertial design

Actuator Mechanics

Larger magnets
Air turbulence controls
RV sensors and closed loop RV
suppression

Smaller magnets
No air turbulence compensation
No RV sensors or suppression – limited to
servo wedge track alignment

Electronics

Dual processors
(dedicated servo and data path processors)
Performance optimization
Advanced Error Handling
Advanced firmware algorithms

Single processor

No performance optimization
Standard Error Handling
Standard Firmware algorithms

Customization

FW Code

Extensive

Limited

Variable Sector Sizes

Yes

No

LEDs

Yes

No

Enterprise-class versus Desktop-class Hard Drives (PDF) (Download courtesy of Intel)

Summary – We have outlined just a few factors when choosing the correct server for your environment. It is important to understand that SAS, SATA, Software Raid and Hardware Raid all have their limitations and benefits. In our opinion, when you are in the market for a server, we think it is a better choice to opt for a hardware raid controller and SAS hard drives. Once you purchase and configure your server, it is not an easy task to go from a software raid to a hardware raid later on down the road when your business expands. On the other hand, it is possible to have a software raid configuration and have SAS hard drives, giving you the operational performance of SAS drives. Whichever choice you make, it is always important to have a working backup in case of a failure.

If you would like to consult with rhinotech or need help picking out a server that is right for your budget and environment contact us today.