IBM System Storage DS4000, Hardware Manual

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IBM Midrange System Storage Hardware Guide
When the controller loses power and dirty data is in the cache, the backup process starts
(copying data from cache to flash memory). If power is restored by the time the backup is
complete, normal operations continue. If power is
not
restored by the time the backup is
complete, the controller disables the batteries and powers off. When it powers on, any dirty
data in flash memory will be copied to cache. Host I/O is supported while backup data is
being restored. Normal power up continues as well. Restored data is immediately scheduled
to be flushed to disks.
Data flow
Figure 3-10 shows a simplified data flow from host port to disk drive (not covering the data
cache flow). This diagram shows the configuration where an array is built on one disk
enclosure and two disks ports are used for I/O operations to one volume. If there are two
volumes on the same array, the second one can be managed by controller B. For each
volume you set, the default controller will manage it, which allows you to evenly load both
controllers and all ports. In this example, there is a RAID 5 array group defined on five drives
and one volume with the default controller A (preferred ownership) and a segment size of
256 KB. There is a 1 MB write request. Drives 1, 3, and p (parity) use port 8 in controller A
and drives 2 and 4 use port 1 in controller B.
Figure 3-10 Data flow with one enclosure
Note: Both data cache as well as flash memory are CRC protected.
Encl 1
Encl 2
Encl 3
Encl 4
Encl 5
Encl 6
Encl 7
Encl 8
7 6 5 4 3 2 1 8 7 6 5 4 3 2 1 8 7 6 5 4 3 2 1
Quad-Port
4 Gb FC
8 8 7 6 5 4 3 2 1
Quad-Port
4 Gb FC
Interconnect Board
Controller A Controller B
Mirror Mirror
Host Ports Host Ports
Loop Switch
Detail
1 MB
HIC HIC HIC HIC
1 MB
.256
KB
(2,4
)
.256K
B
(1,3,p
)
.256KB
(1,3,p)
.256KB
(2,4)
Data Layout
1 2 3 4 p Enclosure 1
1,3,p
7 6 5 4 3 2 1 8 7 6 5 4 3 2 1 8 7 6 5 4 3 2 1 8 8 7 6 5 4 3 2 1
1,3,p
Quad-Port
4 GB FC
Quad-Port
4 GB FC
Quad-Port
4 GB FC
Quad-Port
4 GB FC
Quad-Port
4 GB FC
Quad-Port
4 Gb FC
Quad-Port
4 GB FC
Loop
Switch
Loop
Switch
Loop
Switch
2,4 2,4
Loop
Switch
Loop
Switch
Loop
Switch
Quad-Port
4 Gb FC
Quad-Port
4 Gb FC
Quad-Port
4 GB FC
Quad-Port
4 GB FC
Loop
Switch
Loop
Switch
Loop
Switch
Loop
Switch
Loop
Switch
Loop
Switch
Zip Zip
Processor
Zip
Zip
Processor