Table 9-2 Cache Transition States - Sun Microsystems StorEdge T3+ Installation And Configuration Manual

Four cache modes are supported: auto, write-behind, write-through, and none. The
default mode for the Sun StorEdge T3+ Array is auto.
In the auto cache mode, the caching mode is write-behind if the array has full
redundancy available. If any component is nonredundant, the cache mode is set
to write-through. Read caching is always performed. This mode provides the best
performance while retaining full redundancy protection.
The write-behind cache mode forces write-behind caching to always be used. Data
loss may occur in this mode if the units are not configured as a fully redundant
enterprise and an array system failure occurs.
Caution – To avoid data loss in the write-behind cache mode, make sure you use
host-based mirroring.
The write-through cache mode forces write-through caching to always be used.
Read caching is also performed in this mode.
The none cache mode forces no write caching and no read caching.
Caution – If one of the redundant components fail, the cache mode is set to
write-through. In the write-through mode, mirroring is not used and data is not
being cached. If you were to view the cache mode at this time using the vol mode
command, the setting for cache would be displayed as writethrough and the
setting for mirror would be displayed as on. This means that mirroring is enabled,
but it is not being used.
The following table highlights the system states that can disable write-behind cache.
In cases where write-behind cache has been disabled, the array is designed to protect
the data in cache. If any hardware component fails that might compromise the safety
of this data, the array will disable write-behind cache, causing outstanding cached
data to be flushed to disk. Write-behind caching is
re-enabled when the failed condition has been corrected.
TABLE 9-2
Failure or Problem
Disk hard failure (RAID 5)
Disk hard failure (RAID 1)
Disk hard failure (RAID 0)
Disk reconstruct
Disk copy-back operation
Interconnect card 1
130 Sun StorEdge T3+ Array Installation and Configuration Manual • April 2002
Cache Transition States
Write-Behind Cache State
Disabled
Disabled
Disabled
Disabled
Disabled
Disabled