How is data written to the data drives - is it spread across them?

[mainart1955]

While doing research to build a new Unraid server for my home and small business, I'm hitting some questions.  One area is disks - I could get higher capacity disks like 12TB or smaller capacity like 4TB.  For a while, at least a year or likely longer, I could start with four 4TB drives (12TB data) such as Ironwolf at $75 and could buy a spare too.  Or I could go with 12TB Exos manufacturer recertified drives at $110 and could get up to four of them.  

 

So say I buy four of the 12TB Exos drives. I could:

(A) start with two 12TB drives in the system, keeping two as spares and adding more with failures or growing storage needs, Or,

(B) put all four in at the start and buy more to replace failed ones along the way. 

 

How is say 6TB of data stored in case (A) vs case (B)?  If there are four drives does Unraid spread storage across them or does it fill one drive first then start filling the others?

 

Alternately buy four or five new 4TB Ironwolf drives and

(C) put four in the new system right away, or

(D) put 2 or three in and save the rest as spares or expansion

 

 

Is it always better to buy and install the biggest capacity you can afford - even if there's a possiblity it will be unused for a long period?

 

 

[JonathanM]

1 hour ago, mainart1955 said:

If there are four drives does Unraid spread storage across them or does it fill one drive first then start filling the others?

Depends.

https://wiki.unraid.net/Manual/Shares#Allocation_method

[mainart1955]

Ok, it looks like there are different ways data can be stored.  What is recommended based on useage, disk sizes, number of disks, MTBF etc.   There are going to be tradeoffs like using more smaller disks has a higher chance that some drive will fail, but a smaller amount of data is on the failed drive.  Having a lower number of drives means a lower chance of a drive failure but when one does fail more data is at risk. 

 

Example - which is better:

 

System 1 has four 4TB drives (12TB data, 4TB parity).

System 2 has two 12TB drives (12TB data, 12 TB parity).

Edited May 12, 2023 by mainart1955

[BRiT]

Keep in mind that you probably don't want to buy your drives all at once. This is to prevent them failing all at once or from the same issue IF there is a bad batch or a batch has a common issue.

 

 

 

[JonathanM]

No simple answers, other than fewer drives = less power = less heat.

 

Unraid parity (or any RAID redundancy for that matter) is not backup, it's hardware redundancy. It doesn't protect against any of the common issues like accidental or malicious deletion or corruption.

 

You need to plan for a versioned backup of any data that is important to you.

 

I know you didn't ask about backups, but drive reliability and failures are only a small part of keeping data safe and available.

[mainart1955]

9 hours ago, JonathanM said:

No simple answers, other than fewer drives = less power = less heat.

 

Unraid parity (or any RAID redundancy for that matter) is not backup, it's hardware redundancy. It doesn't protect against any of the common issues like accidental or malicious deletion or corruption.

 

You need to plan for a versioned backup of any data that is important to you.

 

I know you didn't ask about backups, but drive reliability and failures are only a small part of keeping data safe and available.

 

Are you saying unraid should not be used for backups?  Since unraid, RAID, or other NAS, can get huge what would you use for backups of the arrays?

[JonathanM]

1 hour ago, mainart1955 said:

Are you saying unraid should not be used for backups?

Not at all, Unraid is ideal for keeping a backup of your important files. Backup means a SECOND copy of something, if it's the only copy, it's by definition not a backup.

 

If you keep the ONLY copy of a file on Unraid, then yes, you need to figure out a second place to keep a backup copy. Some people upload to a cloud storage provider, others have 2 arrays, some have USB attached drives that they update periodically and keep in a safe place while not being actively updated.

 

You get to decide how important a file is, and what level of protection you want for it. Some of your files that are easily recreated from the originals, like Blu-Ray rips, there is no need to keep a second copy. Family photos however, they probably need need MULTIPLE backups, probably follow the 321 strategy, 3 distinct files on 2 different devices and 1 offsite, so a catastrophic event like a flood or fire is still recoverable.

[mainart1955]

8 minutes ago, JonathanM said:

Not at all, Unraid is ideal for keeping a backup of your important files. Backup means a SECOND copy of something, if it's the only copy, it's by definition not a backup.

 

If you keep the ONLY copy of a file on Unraid, then yes, you need to figure out a second place to keep a backup copy. Some people upload to a cloud storage provider, others have 2 arrays, some have USB attached drives that they update periodically and keep in a safe place while not being actively updated.

 

You get to decide how important a file is, and what level of protection you want for it. Some of your files that are easily recreated from the originals, like Blu-Ray rips, there is no need to keep a second copy. Family photos however, they probably need need MULTIPLE backups, probably follow the 321 strategy, 3 distinct files on 2 different devices and 1 offsite, so a catastrophic event like a flood or fire is still recoverable.

 

Ah, okay thanks for the clarification.  I had planned for using the Unraid array for backups of some other devices too. 

[Hoopster]

3 hours ago, mainart1955 said:

I had planned for using the Unraid array for backups of some other devices too.

This is very common.  I backup three other computers with an Unraid Backup share as the destination. 

 

As far a backing up Unraid array content, I have a backup Unraid server with a copy of main server content, external USB drives and a cloud backup.  I am too lazy to rip discs again, so I would rather have them backed up as well.  If I lost the 10s of thousands of family photos and videos my wife has taken, she might look for a new IT guy.