Enterprise-class versus Desktop-class Hard Drives

Enterprise-class versus Desktop-class Hard Drives
Revision 1.0
9
1.1.4.6 Variable Sector Size
Many enterprise class hard drives (especially SCSI and SAS hard drives) have the ability to
vary the sector size within limits. These drives utilize a 528 byte sector and allow the I/O
controller (usually a RAID controller) to set the data portion of the sector to 512 bytes and to use
the remaining sector capacity for a sector checksum. This allows the I/O controller to verify the
sector data against the checksum and to recover data on the fly from the checksum. The I/O
controller can track this error and remap bad areas of the drive in I/O controller memory. The
drives have the ability to track and remap errors via sector parity.
Desktop (IDE and SATA) drives do not utilize a variable sector size. The sector is locked at 512
bytes, although there is a small area reserved for parity at the end of each sector. This parity is
sufficient to detect an error, but it does not contain sufficient data to rebuild the sector or recover
data if the sector is unreadable. It can only be used as part of the drives internal error detection
mechanism.
Some SATA drive vendors are working to implement variable sector size capability in their
enterprise class SATA drives. Larger sector sizes are forecasted for future implementation.
1.1.4.7 Feature Review
The following table provides a comparison of feature differences between enterprise-class and
desktop-class hard drives. Vendor implementation of these features vary between drive models.
Generally the high end of the feature spectrum includes enterprise-class SAS hard drives, and
the low end includes desktop-class SATA drives. Enterprise-class SATA drives fall somewhere
in between.
Table 1: Feature Reference
Drive Comparison Table
Feature Enterprise Desktop
Spindle Motor
Higher RPM Moderate to lower RPM
Tighter run-out (spindle end movement) Lower specification for run-out
Spindle anchored at both ends Spindle anchored at one end
Media
Full media cert Lower media specification and density
Head Stack Assembly
Structural rigidity Lighter weight design
Lower inertial design Higher inertial design
Actuator Mechanics
Larger magnets Smaller magnets
Air turbulence controls No air turbulence compensation
RV sensors and closed loop RV
suppression
No RV sensors or suppression - limited to
servo wedge track alignment
Electronics
Dual processors (dedicated servo and
data path processors) Single processor
Performance optimization No performance optimization
Advanced error handling Standard error handling
Advanced firmware algorithms Standard firmware algorithms