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D a t a D i r e c t N e t w o r k s S 2 A 9 5 5 0 U s e r G u i d e

The

AV ERR=ON|OFF

command specifies what the Early Error Recovery (EER) bit will be set to on

the drives when DISKAV is enabled. When enabled, the disks disk shall perform the most expedient
form of error recovery first. When disabled, the disks will use an error recovery procedure that
minimizes the risk of mis-detection or mis-correction. The parameter is located in bit 3, byte 2 of the
Read-write error recovery mode page on the disks. The EER of each disk will be set to its default
value when

DISKAV=OFF

. Note that changing the disk parameters can adversely affect the I/O

operation of the system. This parameter should only be adjusted when the system is idle. Default
setting is ON.

The

AV READRETRY=X

command specifies what the read retry count will be set to on the drives

when DISKAV is enabled. This field indicates the number of times the disks will attempt its recovery
algorithm during a read operation. This parameter is located in byte 3 of the Read-write error
recovery mode page on the disks. The retry count of each disk will be set to its default value when

DISKAV=OFF

. Note that changing the disk parameters can adversely affect the I/O operation of the

system. This parameter should only be adjusted when the system is idle. Default setting is 1.

The

AV WRITERETRY=X

command specifies what the write retry count will be set to on the drives

when DISKAV is enabled. This field indicates the number of times the disks will attempt its recovery
algorithm during a write operation. This parameter is located in byte 8 of the Read-write error
recovery mode page on the disks. The retry count of each disk will be set to its default value when
DISKAV=OFF. Note that changing the disk parameters can adversely affect the I/O operation of the
system. This parameter should only be adjusted when the system is idle. Default setting is 1.

The

AV ORDEREDQUEUE=X

command enables the S2A9550 to use ordered tags when

communicating with drives. The value “x” correlates to percentage of ordered tags. 0 indicates no
ordered tags, 1 indicates 100 % ordered tags, 2 indicates 50 % ordered tags, 3 indicates 33 % ordered
tags, 4 indicates 25 % and so on. Valid range is 0 to 255. Default value is 0.

The

AV DISKUPDATE

command tells the system to recheck all of the mode parameters for the disks

in the system. This allows the user to update the disk mode parameters after changing several of the
AV parameters instead of changing them one at a time.

3.3.3

Locking LUN in Cache

The S2A9550 provides the ability for the administrator to lock LUNs 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 S2A9550 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 which has been locked in
cache, the following will occur:

• S2A9550 reads data from disks

• S2A9550 locks data in cache

• S2A9550 sends data to host

• Any reads of the same data will be serviced from cache, which provides faster access than

reading from disks

50% of Data Cache used

to service Locked LUNs

50% of Data Cache used

to service Unlocked LUNs

Initial Cache