Serial ATA Flash Drive
AP-SRFD255AXXXXR-G
9
© 2008 Apacer Technology Inc.
Rev 0.2 (Preliminary)
2.6 Virtualization
Virtualization is a mechanism, where the HBA can have an alternate view of the physical drives. The RAID
Processor allows various access strategies to the connected Hard Disks and may be configured to represent
n-drives as m-drives to the user. This provides the user with a simple way of partitioning storage resources
according to use. For example, the processor could represent one drives as a single, large drive. Another
option would be to make virtual storage resources according to reliability or performance requirements. One
virtual target could be a mirrored set consisting of drives 1 and 2, or could be a striped set consisting of drives
1 and 2. Representing multiple device targets may only be performed with port multiplier aware host
controllers.
2.7 Modes
SRFD supports 2 modes: Fast (RAID-0) and Safe (RAID-1).
2.7.1 Fast (RAID-0) Mode
RAID 0 - RAID Level 0 is not redundant, hence does not truly fit the "RAID" acronym. This method splits the
data over numerous drives but is seen as one drive by the operating system. If one drive fails though, all data
becomes inaccessible. This level is commonly referred to as striping.
The RAID Processor supports a definition of Fast (RAID-0) set. The stripe size (chunk size) is set to 8 KB. The
HBA (Host Bus Adapter) does not need to know anything about the physical arrangement of the data. To the
HBA, the virtualized drive behind RAID Processor is a simple (normal) drive that just happens to be faster. All
error handling etc. is managed by the Processor. The advantage of striping is double the data transfer
throughput of a single physical drive. This applies to both read and write operations.
2.7.2 Safe (RAID-1) Mode
RAID 1- Mirrored Set (2 disks minimum) without parity. RAID-1 set is a combination of two physical partitions,
where the data is “mirrored” among them. Provides fault tolerance from disk errors and single disk failure.
Increased read performance occurs when using a multi-threaded operating system that supports split seeks,
very small performance reduction when writing. Array continues to operate so long as at least one drive is
functioning.
