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-backcaching - the controller sends a data transfer completion signal to the host when the controller cache receives all the data in a transaction.

■Write-throughcaching - the controller sends a data transfer completion signal to the host after the disk subsystem receives all the data in a transaction. Write-throughcaching is the default setting. Write-throughcaching has a data security advantage over Write-backcaching. Write-backcaching has a performance advantage over Write-throughcaching, but it should only be enabled when the optional battery backup module is installed.

Do not use write-back caching for any logical drive in a Novell

Caution

NetWare volume.

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.

170

www.gateway.com