What size can I expect (Tried using the calculator but I'm not 100% sure...)

[markswift]

Hi Guys,

 

Am I right in saying that unRAID will use the largest drive for parity? I tried using the capacity calculator (http://goo.gl/OZ3ibZ) but it didn't seem to reflect the changes I made...

 

I currently have 5 x 3TB WD Red's running on Stablebit's Drive Pool software, I'm looking to migrate these over to unRAID and also add some additional capacity, potentially 2 more drives. Basically I'm trying to work out the total array size if I add 2 x 6TB drives, or perrhaps just add another 2 x 3TB drives. According to the calculator the 2 6TB drives don't seem to offer any space advantage over adding the 3TB drives and the calculator always shows a total size of 20GB? I tried, 3+3+3+3+3+3+3 and 3+3+3+3+3+6+6.

 

I realise this is probably a stupid question but I'd really appreciate some help...

 

Cheers,

 

Mark

[interwebtech]

1 drive is set as parity (not required but what's the point without it?). It's capacity must be greater than or equal to the largest of the data drives that will be used for the array.  The parity drive's capacity is NOT counted toward available drive space on the array. The rest of the drives can be assigned as data drives and added to the array. The sum of their capacities is the drive space available on the array.

[markswift]

Thanks for the reply,

 

That's what I thought, it seems the calculator doesn't reflect the changes correctly then. So it appears I'll only gain 3TB by adding the 6TB drives, doesn't seem worth it on this occasion, I'll throw in 2 more 3TB's.

[garycase]

Thanks for the reply,

 

That's what I thought, it seems the calculator doesn't reflect the changes correctly then. So it appears I'll only gain 3TB by adding the 6TB drives, doesn't seem worth it on this occasion, I'll throw in 2 more 3TB's.

 

Actually you'll gain 9TB if you buy 2 6TB drives, compared to what you'd have with your current 5 3TB drives.    You can use one to replace the drive that would have been your parity drive;  then you can add the other 6TB drive AND the 3TB unit that would have otherwise been the parity drive to the array ... adding 9TB of additional space.

 

If you simply buy 2 3TB drives, you'll get 6TB of additional space.

 

 

[garycase]

... perhaps it's a bit clearer to simply note this:  The "cost" of fault tolerance in UnRAID is ONE hard drive (for parity).    That drive also puts a limit on how large your data drives can be, since no data drive can be larger.

 

The capacity of the array will be the sum of all of the OTHER drives.

 

If you want to be able to use drives > 3TB, then you should buy a drive of the size you want to be able to use for your parity drive ... 4TB, 5TB, 6TB, 8TB, etc.    If you're happy with 3TB as the maximum size drive you can use, then you can simply use a 3TB drive as parity.

 

[markswift]

Hi Gary,

 

That makes sense... I think on this occasion ROI is the big factor, to gain 6TB I'll spend circa £165, to gain 9TB, it'll cost £380... Perhaps in the future I can look at increasing drive sizes.

 

Really looking forward to migrating and getting started!

[SSD]

Hi Gary,

 

That makes sense... I think on this occasion ROI is the big factor, to gain 6TB I'll spend circa £165, to gain 9TB, it'll cost £380... Perhaps in the future I can look at increasing drive sizes.

 

Really looking forward to migrating and getting started!

 

What you say makes sense for your application. As you are learning, the larger the parity the more the cost of redundancy. An expensive 6T drive as parity that is only needed to support one other 6T drive is expensive, but it does allow you to add higher density storage going forward.

 

You might consider buying 2 4T drives. 4T is 25% larger than 3T, and is at the sweet spot of cost per terabyte, and would allow your remaining drive slots to go farther.

[garycase]

The thing to remember is that at some point, when you want to start using larger drives, you have no choice but to buy ONE drive of the new max capacity you want to use.    That's an inevitable "sunk cost" -- and what you'll gain from that is an extra 3TB of storage (the old parity drive).

 

Remember that if you limit yourself to 3TB drives, then any new drives you buy to expand the array are also limited to that size.    In deciding what size drives you want to be able to use, you should consider the # of SATA ports you have available, and what that means in terms of the ultimate capacity of your array using 3TB drives.

 

Based on the current pricing you noted, I gather you can buy 2 3TB drives for £165, and one 6TB drive for £190, so it costs you an extra £25 to add 6TB using one drive instead of 2 ... an extra £4 per TB.    Whether it's worth that depends on how large you plan to grow your capacity.    If 3TB drives are fine, then stay with a 3TB parity drive.    But what you don't want to do is buy a bunch of 3TB drives that you're going to want to upgrade to larger capacity drives in the not-too-distant future ... if you think that's likely, it's far better to bite the bullet now and get a larger parity drive;  then use larger drives as you expand your system's capacity.

 

[markswift]

The voice of reason, perhaps you're right, it's a time to invest, not to be a tight bugger ;-)

 

I envision I'll need some more TB's in the future - so perhaps I'll bite my lip now and sink some money into that 6TB parity drive!