I know we need both but I'm trying to better understand what benifit a parity gives if you have online backups. I have no experience with all this stuff so just trying to get a better handle on it. To my uneducated mind it seems like you can repair pretty much anything with regular online backups. So not sure what the value of the parity is.

 

Thanks,

Stephen

Edited October 6, 20205 yr by SPOautos

4 minutes ago, SPOautos said:

I know we need both but I'm trying to better understand what benifit a parity gives if you have online backups.

The main benefit of parity (single or dual parity) is to recover from disk failures.  Single parity allows you to recover from one failed array disk and dual parity for two simultaneous array disk failures.

 

Let's say you have a single parity array and 5 data disks and data disk 3 fails.  You can simply pop in another disk and, reading from parity and the other 4 data disks, unRAID will be able to automatically reconstruct the new disk 3.

 

Data backups are essential as parity contains no data whatsoever, it just contains a calculated number that represents the data on every sector of all data disks.  This allows the system to figure out what is missing and rebuild a failed disk with the missing bits.

 

The advantage of data backups is to allow you to recover data from accidental deletion, malware/ransomware and other forms of data corruption, failure of more disks than parity can cover, the inability to properly read all other data disks in a rebuild, other hardware failures that mess up data, etc.

 

The disadvantage to only having a data backup is that you would have to figure out what actual content was stored on the failed disk(s) and restore it manually; unless of course, you maintained a backup server with the same configuration and same number of disks.

 

For more on parity, see this parity wiki.

1 hour ago, Hoopster said:

 

 

The disadvantage to only having a data backup is that you would have to figure out what actual content was stored on the failed disk(s) and restore it manually; unless of course, you maintained a backup server with the same configuration and same number of disks.

 

For more on parity, see this parity wiki.

 

What you said right there is what helped me put it into perspective. Since Unraid copies data across multiple drives, if one failed, with 10Tb of data spread across 3 drives, I'd have no way to know what info was lost. So even if I had a backup of everything, I'd have to replace the bad drive then rewriting all my data, refilling up all 3 drives.....which, assuming that is even possible, from a cloud backup it would take forever  (probably over a week). As opposed to just popping in a disk and letting it redo that one disk.

 

Thank You....That helped me better understand why it's not practical to only have a cloud backup when your storing data across multiple drives. 

 

 

Edited October 6, 20205 yr by SPOautos