Order of Disks in RAID Group for RAID 1_0.
When creating a RAID 1_0 Raid Group, it is important to know and understand the order of the drives as they are put into the RAID Group will absolutely make a difference in the Performance and Protection of that RAID Group. If left to the Clariion, it will simply choose the next disks in the order in which is sees the disks to create the RAID Group. However, this may not be the best way to configure a RAID 1_0 RAID Group. Navisphere will take the next disks available, which are usually right next to one another in the same enclosure.
In a RAID 1_0 Group, we want the RAID Group to span multiple enclosures as illustrated above. The reason for this is as we can see, the Data Disks will be on Bus 1_Enclosure 0, and the Mirrored Data Disks will be on Bus 2_Enclosure 0. The advantage of creating the RAID Group this way is that we place the Data and Mirrors on two separate enclosures. In the event of an enclosure failure, the other enclosure could still be alive and maintaining access to the data or the mirrored data. The second advantage is Performance. Performance could be gained through this configuration because you are spreading the workload of the application across two different buses on the back of the Clariion.
Notice the order in which the disks were placed into the RAID 1_0 Group. In order to for the disks to be entered into the RAID Group in this order, they must be manually entered into the RAID Group this way via Navisphere or the Command Line.
The first disk into the RAID Group receives Data Block 1.
The second disk into the RAID Group receives the Mirror of Data Block 1.
The third disk into the RAID Group receives Data Block 2.
The fourth disk into the RAID Group receives the Mirror of Data Block 2.
The fifth disk into the RAID Group received Data Block 3.
The sixth disk into the RAID Group receives the Mirror of Data Block 3.
If we let the Clariion choose these disks in its particular order, it would select them:
First disk – 1_0_0 (Data Block 1)
Second disk – 1_0_1 (Mirror of Data Block 1)
Third disk – 1_0_2 (Data Block 2)
Fourth disk – 2_0_0 (Mirror of Data Block 2)
Fifth disk – 2_0_1 (Data Block 3)
Sixth disk – 2_0_2 (Mirror of Data Block 3)
This defeats the purpose of having the Mirrored Data on a different enclosure than the Data Disks.