ITEM: AI9507L

7135 dual active controller drive groups

Question:

Question on 7135 dual raid controller, what is the meaning of info
in the smit screen?
 Response:

ENV: AIX 3.2.5 scarray.obj 3.3 (dual active 7135) with two controllers
on a 7135-110.

DESC:

Customer is running "smit dacc_chgdev" to change which dac "owns" 
an hdisk (actually a drive group) and after pressing F4 on the
"Select Drive Group to Switch" field he sees something like:

                      Change/Show a Disk Array Controller

Type or select values in entry fields.
Press Enter AFTER making all desired changes.

                                                       [Entry Fields]
  IBM 7135 SCSI RAID Controller                       dac0
* Select Drive Group to Switch                                        +

  lqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqk
  x                       Select Drive Group to Switch                x
  x                                                                   x
  x Move cursor to desired item and press Enter.                      x
  x                                                                   x
  x    0 hdisk2  Raid 5 00-03-00-00 4000 MB Status OPTIMAL            x
  x    0 hdisk3  Raid 5 00-03-00-01 3670 MB Status OPTIMAL            x
  x    1 hdisk4  Raid 0 00-03-00-02 9587 MB Status OPTIMAL            x
  x                                                                   x
  x F1=Help                 F2=Refresh              F3=Cancel         x
F1x F8=Image                F10=Exit                Enter=Do          x
F5x /=Find                  n=Find Next                               x
F9mqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqj

To understand this one needs to understand the concept of a drive group.

A Drive Group is a group of disks that a LUN or sub-LUN exists on.  
Once a LUN is created, the physical disks are put into a group.  If a 
LUN is created one uses all the space on the disks such that we cannot
create another LUN on the group.  If a sub-LUN is created, we can
create another sub-LUN on the drives in this group, with the restriction
that all the LUN parameters (except for size) must be the same (this
includes the RAID level, segment size, etc).  

In the above example, hdisk2 and 3 are in the same drive group (0) and
are sub-LUNs.  hdisk4 is in drive group 1.  Both drive groups (and 
their hdisks) are owned or controlled by dac0.  Once a drive group
is switched to another dac the drive group number may change!  The
hdisk numbers will not change.  Also note that for 2.0 GB disks
the default size of a RAID-5 LUN is 7670 MB, and since the size of
hdisk2+hdisk3 = 7670 MB, we know there is no free space on the drives
to create another sub-LUN.  hdisk4 is a RAID-0 LUN, and uses all
the space available on 5 drives resulting in 9587 MB of space.



Support Line: 7135 dual active controller drive groups ITEM: AI9507L

Dated: May 1995 Category: N/A

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