parity drive question?

[exwarace]

Hi i am building new unraid server and i have question is it recommend to get parity largest drive and data drive can be small?

 

example parity drive 8T data drive 4t

 

Or is it better get 2 8T?

[trurl]

Parity must be at least as large as the largest single data drive. Other than that, you can mix drives of different sizes as much as you want.

 

How much capacity do you expect to need in the next few years?

[c3]

On a new unRAID server (all new disks) parity size is equal to data size. ie, all 6TB or all 8TB.

 

Later, a new 12TB comes out, and you get a black Friday deal, the 12TB goes in as parity before any data can be 12TB.

Edited August 31, 2017 by c3

[trurl]

1 hour ago, c3 said:

On a new unRAID server (all new disks) parity size is equal to data size. ie, all 6TB or all 8TB.

Not sure what you intended with this statement. Of course you know that there is never any requirement for all drives to be the same size, whether the server is new or not.

[c3]

3 minutes ago, trurl said:

Not sure what you intended with this statement. Of course you know that there is never any requirement for all drives to be the same size, whether the server is new or not.

I did not mean that all disk need to be the same size (or new), rather the typical new build has all new drives, and typically all of them are the same size. I think it is unlikely that someone would purchase drives of differing sizes for a new unRAID build, but it can certainly happen.

Certainly, many have inserted various on-hand drives in the initial build.

 

For example, if I was building a new unRAID, it would have all 8TB drives.

 

As you asked, how much capacity is needed? let's say 20TB. Would you really buy (4) 8TB and (1) 4TB? or just (5) 8TB?

That's (2) parity + (3) data, 8+8+4=20TB or 8+8+8=24TB

And if 6TB is the deal of the day/week/month, (5) 6TB and (1) 2TB or just (6) 6TB?

That's (2) parity + (4) data, 6+6+6+2=20TB or 6+6+6+6=24TB

[DanielCoffey]

Remember you don't have to have two parity drives either. One is sufficient for most smaller arrays unless the data really is critical.

 

The parity drive must be as big as (or bigger than) your largest data drive. Beyond that, you can have as many smaller drives in the array as your license allows.

[SSD]

1 hour ago, DanielCoffey said:

One is sufficient for most smaller arrays unless the data really is critical.

 

I think you're sipping too much unRAID cool aid!  Single parity protects you from about 94.73% of failures. The second parity protects an additional ~0.26% to ~94.99%. More parities (if they were supported) would get you closer and closer to 95% but not beyond. Why? Because, as drives / controllers fail, they can and do corrupt parity. And if a failing drive or controller corrupts one parity, it corrupt all parities. So no number of parities are going to be able to protect your critical data from the very real chance of parity corruption, which I estimate happens about 5% of the time.

 

If your data is really critical, you need BACKUPS. Second parity is a completely false sense of security. If you have a very big array (20+ disks) maybe it makes sense. But for a small, average, or even relatively large array it is better to invest in a security system or a fire extinguisher. Because your chances of losing your data to fire is higher than the chances that your second parity is going to save your data. If you willing to buy a parity2 disk, buy it and back up your most critical data. Put it in a safe place like a safety deposit box or a family member's home. It is FAR more likely to save your bacon than using it as parity2.

 

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