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Chapter 6: Configuring your RAID solutions
12 Select the Write Policy from the list to set the write and cache policies. The write policy
parameter specifies the cache write policy.
You can set the write policy to:
■ Write-back caching - the controller sends a data transfer completion signal to the
host when the controller cache receives all the data in a transaction.
■ 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 is the default setting.
Write-through caching has a data security advantage
over
Write-back caching. 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.
13 Select the Cache Policy from the list. The cache policy applies to I/O on a specific logical
drive. It does not affect the read ahead cache.
The options are:
■ Cached I/O - buffers all reads in cache memory.
■ Direct I/O - does not buffer reads in cache memory. When possible, Direct I/O does
not override the cache policy settings.
Direct I/O transfers data to cache and the
host concurrently. If the same data block is read again, the host reads it from cache
memory.
14 Select the Span from the list.
Enable or disable the spanning mode for the current logical drive. If spanning is
enabled, the logical drive can occupy space in more than one array. If spanning is
disabled, the logical drive can occupy space in only one array.
For two arrays to be spannable, they must have the same stripe width and must be
consecutively numbered. If these criteria are not met, the utility ignores the Span
setting.
Spanning lets the logical drive stripe across multiple arrays. Using this option enables
the use of RAID 10 and RAID 50.
Caution
Do not use write-back caching for any logical drive in a Novell
NetWare volume.
8510702.book Page 170 Thursday, July 7, 2005 11:21 AM