VDI Home Directory Sizing

To focus on IOPs or not to focus on IOPs that is the question?  As I sort out a new sizing dilemma I’ve run into a potential problem with SATA drives and IOPs contention.

The Scenario:

Storage Array: NetApp 6280, Data ONTAP 8.1.1, 3TB SATA, DS4243 Shelves, 10% Aggr Snap Reserve (Why? Because wafl iron rebuilds take a fraction of the time with Aggr snapshots)

User Home Directories: 20GB allocated to each user with 20% snapshot overhead

Disks TB / Disk IOPs / Disk
72 1.86 75
TB / Aggr GB / Aggr IOPs / Aggr
134 123,494.40 5400
GB / User Users / Aggr IOPs / User
24 5145 1.05

This leaves me with 1.05 IOPs per user.  A couple things to make note off, this assumes 100% concurrency ie. all 5,145 users accessing this volume at the same time which is highly improbable.  If 75% concurrency is plugged in the IOPs per user grows to 1.4 which seems more reasonable.

Concurrency 75% Concurrency Users IOPs / User
75% 3858.75 1.40

The assumption is that 25% of the user accounts within any organization are for temporary users who are not logged in on a consistent basis.

Possible Solutions to the potential IOPs performance shortage: Since it’s a NetApp array write performance can only be improved by either adding flash pools, upgrading to a higher performance controller, or by adding spindles/disk.  For read performance addition of flashpools, flash cache (read only),  or additional spindles would add performance.

Concurrency 75% Concurrency Users IOPs / User
75% 3750 1.44

Making the numbers more “round” yields a slight difference in IOPs / User.  This issue will be exacerbated with 4TB SATA and future large capacity drives.

Switching gears… Porsche True Cost of Ownership

After a long hiatus from blogging I’m going to attempt to get back into it.  For now I thought it might be interesting to document what it costs to buy and more importantly maintain a “cheap” Porsche.  Many people including myself want to buy a Porsche.  The associated price range for the car itself is varied.  My target car was a 997.1 or a 997.2 with a purchase price of $40k – $50k.  

With this price range there is a large number of cars to choose from.  As the price goes up the mileage of prospective cars generally goes down while the year goes up.  As a rule each year newer brings withit roughly $5k higher price.  Overall I’ve noticed that the lower mileage Porsches command a higher price since they are essentially garage queens, driven on weekends and babied by their owners.  

Car Profiles:

  • Low mileage (under 20k) babied – Potential Problems: IMS Bearing (High), Rubber & Tire Rott (Med.), RMS Leak (High)
  • Mid mileage (20k – 40k) daily / occasional driver – Potential Problems: IMS Bearing (Med.), RMS Leak (Low)
  • High mileage (40k – 80k) daily driver – Potential Problems: Suspension (Low), Brakes (Med.), Clutch (Med.)

I ended up purchasing the car specked out bellow which falls into the high mileage range:

2005 Carrera S (997.1) 59k Miles

Options: Power Sport Seats, Heated Seats, Bi-Xenon Lights + Washers

Purchase Price: $37.5k

Immediate Maintenance: Replace Suspension due to left rear shock being blown: $500 used suspension, Labor: Free/DIY

Preventive Maintenance

  • Replace Clutch, RMS, IMS with LN Engineering upgraded bearing
  • Resurface Flywheel, Replace Pilot Bearing
  • Replace worn tie-rod ends, replace clutch master cylinder due to torn boot
  • Oil Change, Rebalance Wheels, Perform Alignment

Total Cost Including Labor: $4,100.00

Total cost to get the car sorted and ready for the daily commute: $41.6K

Still in the works, knock out the 60k service which will include the following:

  • Replace Serpentine Belt
  • Replace Spark Plugs
  • Replace Air Filter & Cabin Filter
  • Oil Change (already completed within preventive maintenance)

Wholesale Porsche Parts Sources: Sun Coast Parts or Auto Atlanta Porsche Parts