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Robbie Ferguson

unRAID Capacity Calculator

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I was going to reply yesterday that the calculator was pointless, as all you have to do is add up the size of your data drives.  But, then I noticed that it does make an attempt at coming up with current ratings, etc for the power supply.

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13 hours ago, Spyrule said:

Sorry to revive such an old thread, but I came across this calculator, and the only addition that would be nice would be if you choose to run dual parity.

 

While you apologize for rebirthing an old thread, I absolutely adore that folks are still using the capacity calculator, and it inspires me to enhance it. It was built so long ago that the interface is pretty ... ugly. LOL. I will put it on my to-do list.

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I just used this calculator, its still useful because of the stupid way HDD sizes are labeled!

One tiny request - make the default unit 1TB, I think 250/500GB drives are pretty rare now and they can be added as 0.5 etc. Should be a simple change.

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Hi!

I'm sorry for updating this thread after it remained inactive for quite some time but I just wanted to thank @Robbie Ferguson for this tool he created.

This helped me choose which drive I should select as parity drive and what size my PSU should be not to be either oboxiously overkill nor underpowered.

I'm totally new to unRAID an the only NAS I've been using until now is my Synology DS213J so... switching to unRAID is quite a large hop in several regards, and such small but handy tools make my life easier! :) 

Edited by CiaoCiao

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Hi, I am new to Unraid and after watching every tutorial, I still cannot understand how much storage I need for each of the drives. I'd assume the answer is simple.

I have Synology NAS with 2 HDD (both 4TB each) + 1 SSD (0.5 TB for Cache)

 

Given than all of my data will amount to a total of 6TB (in next 5 yrs), what should be the minimal size of:

Parity HDD?

HDD 1?

HDD 2?

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6 minutes ago, emod said:

Hi, I am new to Unraid and after watching every tutorial, I still cannot understand how much storage I need for each of the drives. I'd assume the answer is simple.

I have Synology NAS with 2 HDD (both 4TB each) + 1 SSD (0.5 TB for Cache)

 

Given than all of my data will amount to a total of 6TB (in next 5 yrs), what should be the minimal size of:

Parity HDD?

HDD 1?

HDD 2?

I haven’t ever used this calculator but in your situation I believe you would just need 3- 3 TB drives. Parity drive just needs to be as big as your largest drive on the array. 

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Posted (edited)
46 minutes ago, SpencerJ said:

I haven’t ever used this calculator but in your situation I believe you would just need 3- 3 TB drives. Parity drive just needs to be as big as your largest drive on the array. 

Thanks for quick response.

 

I'm trying to understand this (and I still do not), to know which HDD to purchase and the price is LITERALLY either $100 for ONE additional HDD (parity) of 3TB or $450 for THREE brand new HDD with each 6TB.

 

Help me understand. 

 

In RAID 1 it's pretty self-explanatory:

HDD 1 with 6TB

HDD 2 with 6TB

If all of my data is 6TB and I want it mirrored, I need two drives to have minimum size of 6TB EACH. Easy.

 

In UNRAID, and with my total data of 6TB, how is it possible to have:

1 Parity HDD = 3TB

1 HDD (the data drive)= 3TB

2 HDD (the data drive)= 3TB

to ensure that ALL of my 6GB data is mirrored?

 

I would assume that 6TB+6TB = 12TB (for mirrroring), so HHD1 and 2 would need to have 6TB EACH, and parity would need to have 6TB.

 

Am I misunderstanding something?

 

This video is informative but doesn't help me (personally) calculate the size: 

 

Edited by emod

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1 hour ago, emod said:

I’m n UNRAID, and with my total data of 6TB, how is it possible to have:

1 Parity HDD = 3TB

1 HDD (the data drive)= 3TB

2 HDD (the data drive)= 3TB

to ensure that ALL of my 6GB data is mirrored?

 

I would assume that 6TB+6TB = 12TB (for mirrroring), so HHD1 and 2 would need to have 6TB EACH, and parity would need to have 6TB.

 

Am I misunderstanding something?

 

In Unraid, data isn’t striped so if you had a 3 TB parity drive and 2 3TB data drives, you would be protected from one HD failure and could reconstruct from the parity drive.  If somehow you had simultaneous double hard drive failure then you would be in trouble. 

 

If you want all of your data mirrored, you would need dual parity meaning you would need 4 total 3TB drives. 2 parity/2 normal hard drives. Or- have a secondary backup solution in lieu of dual parity.

 

This is a pretty good video describing the parity drive and how it works:

 

 

 

 

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Unraid is not RAID. There is no mirroring in the parity array. Each parity disk must be at least as large as the largest single data disk. You can have one or two parity, but neither contains any of your data. Parity PLUS ALL other disks allows the data for a missing disk to be calculated. 

 

This is not really any different than the meaning of parity in other uses. Parity is simply an extra bit that allows a missing bit to be calculated from all the other bits.  So, a single parity disk will allow a single missing disk to be calculated no matter how many data disks there are. An additional parity disk allows two missing disks. 

 

RAID1 is the mirroring you are thinking of. That is one of the options for the cache pool. 

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Posted (edited)

Ah! Now it makes sense. Thanks!

 

Here is the rule summarized. There are three conditions when buying HDD for UNRAID.

 

1.  Determine the total size of all of your files. Let's say this is 6TB.

2. Purchase (or reuse) data HDDs which cumulatively(!) have a total storage of a minimum(!) 6TB. This could be HDDs: 1+2+3TB, 2+4TB, 3+3TB.

3. Purchase ONE parity HDD, whose size must(!) be equal to the largest data HDD. Given examples above (in order of appearance) this could be: 3TB, 4TB, 3TB.

 

UNRAID does NOT mirror the data, meaning it does not create a duplicate of all of your files. At any given time, there is only ONE version of a file across ALL data HDDs.

UNRAID simply enables you to purchase less HDDs, and still be able to recover ONE failed drive - this is done using ONE parity drive.

Parity drive does NOT store the actual file, meaning parity drive will not have a PDF or Word document on it - the parity drive stores only a bit calculation from a summary of all data HDDs. Given above examples, the bits would be summarized across 3, 2 and 2 HDDs.

 

There is an option to have TWO parity drives, but I'll leave that discussion for experts.

 

In my case, I have a small home NAS, with 3HDD slots (2.5 or 3.5), and 2 SSD slots (M.2 factor) on Motherboard. So my configuration will be 1 parity HDD (6TB, which I will need to purchase), and two HDD (each 4TB, which I already have). I will have a total of 8TB capacity for all my files. Given that all of my files have cumulative 4TB size, I will have 4TB of additional storage free, which should last me for few years. So, instead of purchasing several new drives worth cumulatively anywhere between $750 and $1,200, I will only need to purchase ONE drive of $150.

 

I decided to purchase parity drive of 6TB, which will enable me to upgrade my future data needs to 12TB (e.g. 4+8TB of data HDDs) if I ever went that far with my data.

 

I buy only HGST HDDs, which are more expensive but have the lowest HDD failure rate (according to Backblaze). Every single Seagate and WD HDD I bought always failed within 1-2 yrs (the former being by far the worst). Not one HGST drive I bought ever failed, and I have one that has been running for 8 years now.

Edited by emod

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