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Controller Management
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RC=ON|OFF enables the Read Continuous (RC) option for Audio/Video streaming data; the system
starts the data transfer for read operations after RCTIMEOUT is reached, even if the disks commands
have not finished. Use this to reduce the latency for read operations in Audio/Visual environments where
latency is more important than data integrity. This parameter is saved on a per-LUN basis. Use in
combination with the LUN=x parameter to change the settings for a single LUN. Enabling this feature
automatically enables FASTAV.
WARNING! This feature allows the system to return invalid data to the initiator.
RCTIMEOUT=x Default setting: disables the Read Continuous option for Audio/Video streaming data.
Note: This parameter is saved on a per-LUN basis. Use in combination with the LUN=x parameter to
change the settings for a single LUN.
LUN=x sets the host command timeout for the Read Continuous option for Audio/Video streaming data.
Set to 0 to disable the Read Continuous feature in the system. This value is in 100 millisecond
increments. The range for 'x' is 0 to 255. The default is 8.
FAILCC=ON instructs the host ports to report a check condition for all SCSI commands when the unit
is in a failed state. This command should only be used in AV environments when a check condition is
required instead of taking the unit off the loop.
FAILCC=OFF This is the default setting. Host ports will NOT report a check condition for all SCSI
commands when the unit is in a failed state.
3.3.3 Locking LUN in Cache
Locking a LUN in data cache will keep all of the data for the LUN in the cache for faster access. Once
a LUN is locked, the data that is gathered to service read and write commands will stay permanently in
the cache. The controller will continue to fill up the cache until 50% of the total cache is filled with data
from locked LUNs, while the other 50% of the cache is reserved to service I/O for unlocked LUNs.
For example, when a host issues a read command for data from LUN 1 that has been locked in cache, the
following will occur:
• The controller reads data from disks, locks data in cache, and sends data to host
• Any reads of the same data will be serviced from cache, which provides faster access than reading
from disks.
Once the size of the locked LUNs exceeds 50% of the total cache, the controller must create cache space
to process a new I/O by removing older data from the locked portion of cache. The Least Recently Used
(LRU) algorithm is used to determine which locked data to remove from cache.
50% of Data Cache used
to service Locked LUNs
50% of Data Cache used
to service Unlocked LUNs
Initial Cache
Unlocked LUN data
Unallocated
cache*
Data for
LUN 1
* Unallocated cache can be used for unlocked LUNs’ or locked LUNs’ data.
Once cache has been allocated to a locked LUN, however, it cannot be used
by an unlocked LUN.
Cache allocation after I/O completes