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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.

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Gateway 9715 Bedienungsanleitung Seite 175