I always thought that all harddrives were the same. The only difference was capacity and brand reliability. That all changed when I got into reviewing SQL Server disk performance and accumulating statistics over the past several years, I started getting interested into the different types of storage and testing these different types of storage.
I came across the following spec comparison chart, comparing SAS vs SATA. Incase you didn’t know, SATA is what you typically buy for your desktop PC or laptop. SAS is enterprise grade and usually found is NAS and SAN systems. Bit of a price difference, with SAS hard-drives about 70% more expensive than SATA hard-drives.
In the below table, I have highlighted in RED the major differences that I believe make SAS hard-drives are worth the extra $$$.
| Requirement | SAS | SATA | |
| 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 |
| 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 | Does 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 |
|
| Customization | FW Code | Extensive | Limited |
| Variable Sector Sizes | Yes | No | |
| LEDs | Yes | No | |
Fast disks can make a big difference in performance.
If you don’t have the ability to purchase fast disks then increase the memory on the database server to offset the slow disk. More memory means that SQL Server can cache more into its memory rather than have to go to disk to get the data.
Source: http://www.intel.com/content/www/us/en/support/server-products/000005782.html
1 Giant Nerd 