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Network Raid 5 thin provisioning calculations seem off

taylorb
Advisor

Network Raid 5 thin provisioning calculations seem off

I'm checking some storage utilization figures here and I can't quite make sense of them.    I've got a 3-node P4500 cluster  (SAN/IQ 9.5) at one of our sites and I have used Net Raid 5 on all the volumes.   I have a total of 12.3TB of space across the 3 nodes and I have created volumes with about 8.75TB of usable space.  What is puzzling me is that the "provisionable" space column is showing up as 27TB.   According to the user's guide, that means the volumes I have created could use up to 27TB of space.   I don't get how that is even possible?

 

   Also if I  look at the individual volume usage, it is showing me insane space savings for thin provisioning.   For example I have a 2TB volume with 1.5TB of data and it says I have 3.9TB of space saved through Thin Provisioning.  How is that possible?  It's like it is calculating everything triple.    But then the consumed space shows 2.33TB which is more like what I would expect (1.5x actual disk usage).

 

So I guess, one, is this normal, and two, how do I know how much disk I have really used or what's really available when using a Raid 5 and thin provisioning?

 

Thanks.

 

 

 

 

2 REPLIES
Jess1313
Advisor

Re: Network Raid 5 thin provisioning calculations seem off

Network RAID 5 on the LeftHand systems use a thin NR-10 write layer, then use hidden snapshot schedules to "restride" the data to NR-5. So when they calculate the space full provisioning would use the have to account 1 full layer for NR-10 of the size of your volume, plus the NR-5 snapshot. 

 

In other words dont ever use NR-5 and full provisioning, because as you can see it will take up alot of space. 

 

taylorb
Advisor

Re: Network Raid 5 thin provisioning calculations seem off

So you are saying the "full" provisioning is triple the space for a Net Raid 5?   But it could never actually use that amount, right?    I have nearly full NR5 volumes and they are only using about 1.5x the provisioned capacity, so that seems like worst case scenario.