Administrator Guide

Changing system cache settings

The Cache tab provides options to change the synchronize-cache mode, missing LUN response, host control of the write-back cache

setting, cache redundancy mode, and auto-write-through cache triggers and behaviors.

Changing the synchronize-cache mode

You can control how the storage system handles the SCSI SYNCHRONIZE CACHE command. Typically you can use the default setting.

However, if the system has performance problems or problems writing to databases or other applications, contact technical support to

determine if you should change this option.

Change the synchronize-cache mode

1. In the System topic, select Action > Advanced Settings > Cache.

2. Set the Sync Cache Mode option to either:

• Immediate. Good status is returned immediately and cache content is unchanged. This is the default.

• Flush to Disk. Good status is returned only after all write-back data for the specified volume is flushed to disk.

3. Click Apply.

Changing the missing LUN response

Some operating systems do not look beyond LUN 0 if they do not find a LUN 0 or cannot handle noncontiguous LUNs. The Missing LUN

Response option handles these situations by enabling the host drivers to continue probing for LUNs until they reach the LUN to which

they have access.

This option controls the SCSI sense data returned for volumes that are not accessible because they don’t exist or have been hidden

through volume mapping (this does not apply to volumes of offline disk groups).

Change the missing LUN response

1. In the System topic, select Action > Advanced Settings > Cache.

2. Set the Missing LUN Response option to either:

• Not Ready. Sends a reply that there is a LUN where a gap has been created but that it’s “not ready.” Sense data returned is a

Sense Key of 2h and an ASC/ASCQ of 04/03.

• Illegal Request. Sends a reply that there is a LUN but that the request is “illegal.” Sense data returned is a Sense Key of 5h and an

ASC/ASCQ of 25/00. If the system is used in a VMware environment, use this option. This is the default.

3. Click Apply.

Controlling host access to the write-back cache setting

You can prevent hosts from using SCSI MODE SELECT commands to change the write-back cache setting of the system.

Some operating systems disable write cache. Host control of write-back cache is disabled by default, which prevents the host from

modifying the cache setting.

Enabling the host control of write-back cache option is useful in some environments where the host disables the write-back cache.

However, enabling this option might result in degraded performance.

Change host access to the write-back cache setting

1. In the System topic, select Action > Advanced Settings > Cache.

2. Either select to enable or clear to disable the Host Control of Write-Back Cache option.

3. Click Apply.

Changing auto-write-through cache triggers and behaviors

You can set conditions that trigger a controller to change the cache mode from write-back to write-through, as described in About volume

cache options. You can also specify actions for the system to take when write-through caching is triggered.

Working in the System topic