DataDirect Networks S2A9550, Руководство пользователя

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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
M a n a g i n g t h e S 2 A 9 5 5 0
Once the size of the locked LUNs exceeds 50 % of the total cache, the S2A9550 will have to 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.
For example, LUN 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:
• S2A9550 determines which data to remove from locked portion of cache, using the LRU
algorithm:
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 since
it is the least recently used data.
• S2A9550 reads data from disks
• S2A9550 locks data in cache
• S2A9550 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 command: LUN LOCK=x
where “x” is the Logical Unit number <0..127>
(Figure 3-32)
.
To unlock a LUN and release the cache locked by the LUN, enter command
LUN UNLOCK=x
.
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
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.
Figure 3-32 Logical Unit Status - LUN Locked in Cache
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
S2A [1]: lun lock=0
Owner
1
1
1
1
Label