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- The SAN Storage Trinity - October 13, 2017
With Storage, the same design challenge always applies – balancing
- Point 1: Terabyte Capacity
- Point 2: IOP’s Performance – meaning true Random 4KB 75% Read / 25% Write ‘type’ IOPs
- and Point 3: Cost
The above three form the holy trinity of a ‘basic’ Storage Design
![](http://www.cd-datahouse.co.uk/wp-content/uploads/2013/01/disk-drive1.jpg)
Tailored SAN Design
But now lets add other critical aspects which we need to tailor the storage to each customers taste.
![](http://www.cd-datahouse.co.uk/wp-content/uploads/2017/10/Tailored-Fit-Suit-Shirt.jpg)
Overall System Availability
- Do we need a Single Controller / Single Node or Multiple Controllers to handle the failure of a single controller
- In essence 99% of storage proposed is dual controller, unless we are talking about archive systems that could afford to be down for a day or so
![](http://www.cd-datahouse.co.uk/wp-content/uploads/2013/01/availability_02.gif)
Data/Disk Redundancy
- RAID 1/10, RAID5 or RAID 60
- But once we make this selection, we immediately need to revisits Point 2
- Our RAID Selection will critically impact our Write performance
- and in RAID 10, it will at least halve our overall capacity – so we need to revisit Point 1
- and now we need to Revisit Point 3
![](http://www.cd-datahouse.co.uk/wp-content/uploads/2013/01/raid5.png)
Compromise
At this point, we either have to:
- add more Disks to increase capacity and IOPs
- moved to SSD Disks for Performance
- or taken another approach of adding a larger number of 7.2K RPM disks to achieve the same level of IOPS
![](http://www.cd-datahouse.co.uk/wp-content/uploads/2013/01/hard_drives_stack_sm.jpg)
RAID
Introducing RAID, we have likely satisfied our ‘need’ to handle failure of 1, 2 or more disks
- But a failed disk in a RAID needs to be re-built and that rebuild time can grow exponentially
- Plan for 60-70-80 hours for a Rebuild of a 6TB drive in a RAID 6 array
![](http://www.cd-datahouse.co.uk/wp-content/uploads/2013/01/raid_rebuild_percentage.png)
RAID Rebuild Times
Now we have introduced a new problem
- Its possible the RAID rebuild time – and having our data at risk during this rebuild process does not meet our needs
- OK – Lets go back and revisit RAID again – and maybe RAID 50, or RAID60 could alleviate some of the statistical problems associated with disk failure (ie spread, but not eliminate the risk)
![](http://www.cd-datahouse.co.uk/wp-content/uploads/2013/01/RAID_50_thumb.png)
Rackspace and Power Costs
While all of this is going on, the number of disks in our system has likely grown and grown
- Now we have a new problem
- We’re quickly running out of rackspace
- (let alone power or heat issues)
- (let alone power or heat issues)
Storage design was never meant to be easy – its an iterative process, where each change has a knock on effect to each an every other parameter.
![](http://www.cd-datahouse.co.uk/wp-content/uploads/2013/01/serverRack.jpg)
In Closing
Most small businesses visit this challenge once every 4 years.
Its an impossible decision to make and we often see over spend anywhere in the order of 30-40%.
This is justified by: ‘I can always use plenty of extra capacity’.
My take: You’ve likely burnt 30K GBP, 50K GBP , 100K or 200K GBP more than you needed to.
That spend could be put to improving your security, network or data protection position.
If you’re in the middle of a storage refresh and the deciding factor is how much discount you are about to receive, I hope the points above offer some guidance.