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80 Intel
®
RAID Software User’s Guide
Setting Drive Parameters
The following fields are displayed in the VD Definition screen (see Figure 23 and Figure 27 ),
which can be used to set the virtual drive parameters:
•
RAID Level:
— RAID Level 0: Data striping
— RAID Level 1: Data mirroring
— RAID Level 5: Data striping with parity
— RAID Level 6: Distributed Parity and Disk Striping
— RAID level 10: Striped mirroring
— RAID Level 50: Striped RAID 5
— RAID Level 60: Distributed parity, with two independent parity blocks per stripe
•
Stripe Size: Specify the size of the segment written to each disk. Available stripe sizes
are 4, 8, 16, 32, 64, 128, 256, 512, and 1024 Kbytes.
•
Access Policy: Select the type of data access that is allowed for this virtual drive. The
choices are Read/Write, Read Only, or Blocked.
•
Read Policy: Enables the read-ahead feature for the virtual drive. Read Adaptive is the
default setting.
— Normal: The controller does not use read-ahead for the current virtual drive.
— Read-ahead: Additional consecutive stripes are read and buffered into cache. This
option will improve performance for sequential reads.
— Adaptive: The controller begins using read-ahead if the two most recent disk
accesses occurred in sequential sectors.
•
Write Policy: Determines when the transfer complete signal is sent to the host. Write-
through caching is the default setting.
— Write-back caching (Further classified as Write Back with BBU or Always Write
Back, which means Write Back is always enabled even if BBU is bad or missing):
The controller sends a data transfer completion signal to the host when the controller
cache receives all of the data in a transaction. Write-back caching has a performance
advantage over write-through caching, but it should only be enabled when the
optional battery backup module is installed. The risk of using Always Write Back
should be fully recognized.
— Write-through caching: The controller sends a data transfer completion signal to the
host after the disk subsystem receives all the data in a transaction. Write-through
caching has a data security advantage over write-back caching.
Caution: Do not use write-back caching for any virtual drive in a Novell NetWare*
volume.
•
IO Policy: Applies to reads on a specific virtual drive. It does not affect the read-ahead
cache.
— Cached IO: All reads are buffered in cache memory.
— Direct IO: Reads are not buffered in cache memory. Data is transferred to cache and
to the host concurrently. If the same data block is read again, it comes from cache
memory.