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RAID and DDP Technology

November 21, 2016Categories: News. Tags: ddp, dell, raid, storage, and technology.

RAID and DDP technology
RAID or Redundant Array of Independent Disk (also known as Redundant Array of Inexpensive Disk) become a basic requirement to implement server or storage system. RAID give redundancy and performance advantage, besides RAID can create a huge single amount of logical disk from a number of physical disks to accommodate large size disk requirement. Unfortunately to create a RAID needed more disks, needed more cost. The cost increase to buy more disks for redundancy, even 100% for RAID 10. The cost will increase more if hotspare is applied.

People will choose RAID 0 for best performance and huge size logical disk, but it does not have redundancy. If a single physical disk failed, data become unavailable. As equal best performance, RAID 10 could be chosen. But RAID 10 is very expensive since it require to mirror every single physical disk. So the cost for disk redundancy will be double.

As alternative, for system that do not really need best performance, RAID 5 or 6 can be chosen. It can accommodate for redundancy and still sufficient for performance. Between RAID 5 and 6, RAID 5 is better in performance. But RAID 5 only tolerance with one disk failed, in the other hand, RAID 6 can tolerance with 2 disks failed.

In RAID technology, there is a process called rebuild. This process happen while a disk failed in a RAID group. Some people does not aware that during rebuild process, the performance will significantly decrease. Sometimes it cause second disk failed. So that is why a hotspare (HS) is strongly recommended.

Answering those challenge, some vendors develop new technologies. They modify the RAID mechanism to handle redundancy and performance. People know the common RAID as conventional RAID. RAID 0, 1, 5, 6, and 10 are still called conventional RAID. An easy characteristic to be identified is whether the RAID use same size or same type in a group. Whereas the modern RAID has left the characteristic to use same size and same type in a RAID group. So that a modern RAID can mix different disk size and type in a RAID group.

RAID flowchart

Traditional RAID vs. DDP Decision Tree

Currently Dell has a technology whereas from performance and redundancy perspective, in normal operation or during rebuild process, this technology has more advantage. Dell called this technology as Dynamic Disk Pool or DDP.

In Dell technical report, mentioned that DDP feature dynamically distributes data, spare capacity, and protection information across a pool of disk drives. So with this technology, there is no performance degradation during rebuild process while a disk failed. Also, no more cost for hotspare to extend the redundancy. [MRK]

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