APC SGI 15000 RAID - Manual (Page 74)

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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).
3.3.3.1 Locking / 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 ) .
Figure 3–32 Logical Unit Status - LUN Locked in Cache
LUN UNLOCK=x unlocks a LUN and releases its cache locked by the LUN.
3.3.3.2 System Performance Statistics
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