Appx max Budget:

The most you can spend right now on your drives (excluding controllers, etc.)

Parity Drives:

Parity drives: 2=RAID6 or RAIDZ2, 3=RAIDZ3. (This won't calculate mirroring properly nor should you use RAID5, so don't use 1.)

Max drives per stripe:

Max drives per stripe (between 8 and 12 is a good number).

Power Cost/kWh:

Make sure this is accurate for your area. Power charges vary widely.*

Cooling W / Array W

How many Watts of cooling will it cost per drive Watt + addt'l Watt (can be zero if ambient cooled, or negative if drives are heating your house

Assumed drive life (yr):

Feel free to change this, but it must make real-world sense.

Drives / Controller:

This is an average-ish controller capacity. If you're gonna use just on-motherboard ports, it's irrelevant because...

Controller Cost:

Cost per SATA / SAS controller. If you're gonna use just on-motherboard ports, make this zero.

Addt'l Per-drive Cost:

The added one-time cost of a bigger PSU, case, more MB slots, cabling, etc.

Addt'l Per-drive Watts:

The added power required for drive controllers, PSU inefficiency, more cooling fans, etc.

This sheet is all based upon your max budget. Set F21 first.

Generally speaking, as your budget gets higher (and therefore the quantity of drives that

All numbers in a black font are read-only.

you can use in your array increases), the better TCO values will

Fields with a blue background are those you definitely want to change to suit your needs and today's drive costs

trend towards bigger capacity drives. This is due to the lower relative cost of parity

Fields with a purple background are those you probably want to change, or at least verify

Array capacity is marked with a yellow background because it's obviously super important. (But read-only.)

Likewise, a lower budget will probably dictate using smaller capacity drives.

When making this sheet I went in with the budget as the priority, but of course

(Of course, the whole point of this spreadsheet is because those general

you may have a certain amount of storage need, and that may supercede your

statements may not be true for your use case.)

budget requirements. You can tweak the budget until you get a capacity which

suits your needs, or even re-work the sheet to make the capacity the driving number.

IF YOU GET #DIV/0 ERRORS IN SOME ROWS FOR TCO,

I used HDD costs based upon when I created/updated the spreadsheet and the drives I wanted to use.

THAT'S PROBABLY BECAUSE YOUR BUDGET IS TOO SMALL

You should check drive prices right now, because that will make a huge difference.

FOR THE NUMBER OF PARITY DRIVES YOU SELECTED

* Cost/kWh may not be as simple as the cost per kWh listed on your power bill.

FOR THE CAPACITIES THAT HAVE THOSE ERRORS.

For example, my power company levies a seperate "delivery charge" to

You can ignore those errors and just resign yourself to the fact that those drive capacities

cover infrastructure costs, which is based upon usage.

don't make sense for anything except mirroring.. at best.

The "addt'l" costs (fields F29 and F30) are something you're going to have to estimate.

If you don't feel like getting involved in that, TCO/TB (column M) should

give you reasonably good guidance.

Power / Drive is something you'll have to glean from the manufacturer data sheets

for the drive(s) you're going to use. The 6W used as a default is probably

a reasonable number for 5400RPM drives with a lower workload.

Most importantly, play with the numbers.

That will give you a better feel for how each aspect of your proposed

setup impacts the TCO.

HOWEVER!

Remember that this isn't going to be 100% accurate. Small changes in multiple fields

can really impact the TCO. Unforseen things like environmental factors could

also have an effect. (E.g. more drives means more air condidtioning in hot climates.

But, coversely, more drives may SAVE on heating costs in cold climates.)

This sheet is simply for guidance, but you may be surprised at the TCO numbers.

Sometimes the largest drives make for the less efficient configurations,

but not always.

FINALLY, you might of course have your own priorities. E.g. more drives means more

noise, which you might find an overriding factor to cost. Same goes for

space, because obviously a few large capacity drives can be put in a smaller

case. But these numbers may serve to put your priorities in perspective.