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Saturday, September 1, 2012

Exadata sizing updated for 3tb drives 1/2 rack SATA

OK, Now I new Exadata coming in that has 3tb drives, and the first question asked is .. How much disk to I have to configure on it ?  Well I'm going to expand on a previous entry I did on sizing .

1/2 Rack. Sata drives. normal redundancy

This means we have
  • 7 storage cells
  • Each storage cell contains 12 disks
  • each disk is 3tb (which is about 2.794 tb usable)  *** This is calculated using base 1024 
  • The first 2 disks in each storage cell has 29.103g already partitioned for the OS (which is mirrored).
  • The rest of the disks in the group are used for DBFS
Given this, I am going to calculate out the total disk available then subtract out the 29.103g (for OS and DBFS).

First 12 disks * 7 cells x 2.794 = 234.696 tb of total raw storage/
Subtract out 29g* 2 disks * 7 cells = 406g    ----- OS
Subtract out 29g * 10 disks * 7 cells = 2.03tb  -----   DBFS
Available raw is 234.696 - 2.436 = 232.26  

Now I said we were running Normal Redundancy.. This means that we loose 1/2

DBFS = 1.015tb
OS        29g
Remaining for Data and Reco = 116.13

But of course we need to account for cell being off line.  This takes out 1/7 of the storage.

DBFS   === .870 tb (29g * 10 * 6)/2
Everything else  ===  ( 2.765 * 12 disks * 6 cells)/2   == 99.54

So now we have 99.54 raw storage available for Data and Reco.

This is now easy to figure out now.. You have really 100tb raw storage (with normal redundancy) to split up between Data and Reco.

Now a full rack is easy to do.

2.765 * 12 disks * 13 cells) / 2 =  215.67tb 

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