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.
Initial Cache
Unlocked LUN data | Data for | Data for | Data for | |
LUN 0 | LUN 1 | LUN 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).
Cache allocation after I/O completes
Unlocked LUN data
Data for LUN 3
Data for | Data for |
LUN 1 | LUN 2 |
|
|
3.3.3.1Locking / Unlocking a LUN
To lock a LUN in the data cache, enter:
LUN LOCK=X<Enter>
where “X” is the Logical Unit number <0..1023> (Figure 3–32).
15000 [1]: lun lock=0 |
|
|
|
|
|
|
| Logical Unit Status |
|
| |
LUN Label Owner | Status | Capacity | Block | Tiers | Tier List |
|
| (Mbytes) | Size |
|
|
0 | 1 | Cache Locked | 10002 | 512 | 3 | 1 | 2 | 3 |
1 | 1 | Ready | 10002 | 512 | 3 | 1 | 2 | 3 |
2 | 1 | Ready | 10002 | 512 | 3 | 1 | 2 | 3 |
3 | 1 | Ready | 10002 | 512 | 3 | 1 | 2 | 3 |
System Capacity 277810 Mbytes, 237802 Mbytes available.
Figure 3–32 Logical Unit Status - LUN Locked in Cache
LUN UNLOCK=x unlocks a LUN and releases its cache locked by the LUN.
3.3.3.2System Performance Statistics
The controller monitors
The STATS command displays the Performance Statistics for the host ports, disk channels, and cache memory (Figure
60 |
