APC 15000 RAID User Manual

 

60 

007-5510-002

For example, LUNs 0 to 3 are locked in cache and all 50% of the total cache has been filled by data from 
LUN 0, 1, and 2. 

When a host issues a read command for data from LUN 3, the following will occur: 

• The controller unit determines which data to remove from the locked portion of cache, using the 

LRU algorithm.  The LRU algorithm is thus:  If LUN 0 has not been accessed for 1 hour, LUN 1 
has not been accessed for 30 minutes, and LUN 2 has not been accessed for 2 minutes, then 
LUN 0’s data will be removed from cache because it is the least recently used data.

• The controller reads data from disks, locks data in cache, sends data to host.

• Any reads of same data will be serviced from cache (until data is removed from cache due to its 

being the least recently used data). 

To lock a LUN in the data cache, enter: 

<Enter>

 

where “X” is the Logical Unit number <0..1023> (Figure 3–32

)

. 

Logical Unit Status - LUN Locked in Cache

LUN UNLOCK=x unlocks a LUN and releases its cache locked by the LUN. 

The controller monitors pre-fetch and cache efficiency, request distribution, transaction, and transfer 
rates by port. 

The STATS command displays the Performance Statistics for the host ports, disk channels, and cache 
memory (Figure 3–33

. It will show the read and write performance of each of the host ports. 

Unlocked LUN data

Data for 

LUN 2

Initial Cache

Data for 

LUN 0

Data for 

LUN 1

Cache allocation after I/O completes

Unlocked LUN data

Data for 

LUN 2

Data for 

LUN 3

Data for 

LUN 1

Logical Unit Status

Block

Size

LUN

Tiers

Tier List

Capacity

(Mbytes)

512

-------------------------------------------------------------------------

10002

Cache Locked

0

System Capacity 277810 Mbytes, 237802 Mbytes available.

Status

3

1 2 3

512

10002

Ready

1

3

1 2 3

512

10002

Ready

2

3

1 2 3

512

10002

Ready

3

3

1 2 3

15000 [1]: lun lock=0

Owner

1

1

1

1

Label