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RifleJock's RAID cache speculations


RifleJock

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Alright, so... I've got a scenario.

RAID 1 is okay, but I'd prefer a little more IOPS performance in the Write department.

Lets say I have 3 SSD's | with different speed tiers (1 will represent fastest, 3 slowest) R/W = Read or Write | Capacity=GB(s)
1. NVMe         | 1R | 1W | 250GB

2. SATA 3D     | 3R | 2W | 250GB

3. SCSI-USB   | 2R | 3W | 240GB

 

If I were to run RAID 5, you would want the fastest and largest capacity to be the parity correct? so the obvious choice would be to have the NVMe be the parity. But this means that my actual reads would be limited to the two other drives. Not to mention, that I'm still limited to their writes as well. I think RAID 5 (plus the non-100% working features in btrfs) is not a good option here.

 

Can I run RAID 0? Would this choose SCSI (smallest capacity) and what other drive to pair? Can I force it to choose another? What would happen to the 3rd drive?

 

Would you just recommend running RAID 1 and forget about the concepts?

 

What would you do with all of the given options? It doesn't matter too much as I will likely be replacing all of my Cache disks with 2TB SATA SSD's. But I was curious to know all's thoughts.

 

ATM, with nothing running, If I run a scrub. I can see up to 1.5GB/s reads. I know between the drives, their individual capabilities added up would equal around 2,310MB/s Read and at least 1,590MB/s Write.

 

Now that I think about it, I believe there was a plugin to do disk speed tests... I wonder if it does the entire cache.

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