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piedthepiper
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June 13th, 2016 12:00
Usable disk sizing question Compellent
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
piedthepiper
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Posted June 13th, 2016 15:00
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?
BVienneau
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Posted June 13th, 2016 13:00
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.