Usable disk sizing question Compellent

Question

Hi there guys, I had a sales guy tell me: Capacities based on 30% R10 / 80% R5-9. obviously you cant have 30/80 so I am assuming him meant 30/70 which seems to the the average I am having trouble understanding how the usable figure below came about? 1.9TB MRI SSD 24 Disk (23 usable) 93,794 IOPs 32,038GB Usable My calculations which I assume are incorrect: 23 usable drives would give 43.7TB RAW @30/70 write/read   30/70 RAID 10 and RAID 5-9 43.7 x0.3 = 13.11 TB RAW would be used for writes 13.11/2 = 6.55TB usable RAID 10 43.7-13.11=30.59TB left RAW 30.59x0.89=27.2251 usable at RAID 5-9 6.55+27.2251=33.784TB usable  30/70 RAID 10 and RAID 5-5 43.7 x0.3 = 13.11 TB RAW would be used for writes 13.11/2 = 6.55TB usable RAID 10 43.7-13.11=30.59TB left RAW 30.59x0.8=24.472TB usable RAID 5-5 6.55+24.472=31.022TB usable What am I missing? Cheers

BVienneau · Accepted Answer

Marketing vs. Actual Usable per drive numbers likely... A 1.92 TB drive nets you 1788.14 GB of usable space per drive. That will likely adjust your numbers down close to what you were provided.

piedthepiper · Answer

Ah once again your input has been helpful! Thank you that makes more sense.

Since compellent would put all that tlc in one tier, I take it we don't have to worry about having an even number of droves for raid 10 as compellent will just stripe across everything as it sees fit?

Compellent

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