Nimble RAID level

[katbert]

I have new HF20H, initial configuration was made by hardware vendor.

In web GUI I see:

HDD 12.5 TiB Usable (20 TiB / 22 TB Raw) Cache 1.3 TiB Usable (1.3 TiB / 1.4 TB Raw) 

I have 22 1TB drives. But I can't see in web GUI, which RAID level is used?

[Sheldon Smith]

The Nimble OS supports a Triple+ parity RAID schema that tolerates three simultaneous drive failures per bank. 

[katbert]

Using triple+ parity RAID - we pay 4 HDD capacity per bank?

[Cali]

Hi,

sometimes a picture or video can explain this better.

https://youtu.be/fvMb53C-a-w

(Alletra and Nimble use the same Disk Disk Shema).

Cali

[katbert]

Picture says: ~75% raw-to-usable capacity.

But my Nimble WebGUI says: HDD 12.5 TiB Usable (20 TiB / 22 TB Raw) - it's only 62,5% raw-to-usable capacity.

[Sheldon Smith]

There is RAW capacity: The total capacity of the HDDs.
You said 20 TiB

There is USABLE capacity: What is available after applying the Triple+ RAID.
You said 12.5 TiB

There is EFFECTIVE capacity: What you get after inline data deduplication and compression.
It will depend on the compressibility and how much can be deduplicated.

In the video, the Alletra 6000 you see uses 24 SSDs. 24 SSDs is standard for all Nimble and Alletra 6000 all-flash arrays.
The Triple+ Parity RAID is applied across all 24 SSDs,

The HF20H has higher overhead: A HF20H has one or two 11 HDD disk banks, and SDDs for cache. The Triple+ Parity RAID is applied to each 11-disk bank.

[katbert]

The Triple+ Parity RAID is applied to each 11-disk bank.

Many vendors use Triple Parity RAID, for example:

RAID triple parity (RTP) is a new algorithm for protecting against three-disk failures. ... For any number of data disks, RTP uses only three parity disks.

https://www.netapp.com/atg/publications/publications-raid-triple-parity-20123615/

If I have two 11-disk banks - 6 disks works only for triple parity. But Triple+ parity uses additional intra-drive parity. And total overhead is... ?