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40 Configuring the system
Changing cache settings
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.
To change the synchronize-cache mode
1. In the Configuration View panel, right-click the system and select Configuration > Advanced Settings >
Cache.
2. Set Sync Cache Mode 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 vdisks). Use
the default value unless a service technician asks you to change it to work around a host driver problem.
To change the missing LUN response
1. In the Configuration View panel, right-click the system and select Configuration > Advanced Settings >
Cache.
2. Set Missing LUN Response 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. This option is the
default.
• 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.
3. Click Apply.
Controlling host access to the system's write-back cache setting
You can prevent hosts from using SCSI MODE SELECT commands to change the system's write-back cache
setting. Some operating systems disable write cache. If host control of write-back cache is disabled, the
host cannot modify the cache setting. The default is Disabled.
This option is useful in some environments where the host disables the system's write-back cache, resulting
in degraded performance.
To change host access to the write-back cache setting
1. In the Configuration View panel, right-click the system and select Configuration > Advanced Settings >
Cache.
2. Either select (enable) or clear (disable) the Host Control of Write-Back Cache option.
3. Click Apply.