1 or 2 parity drives with 4x WDC 10TB HDD


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Do you have full backups of all important data already in place and a strategy to keep them updated?

 

If not, then the extra drive would be much better as a backup drive. Parity will help with keeping your array up and running when a drive fails, and dual parity can be valuable if you have a second failure while you are rebuilding the first failure, but it won't get deleted or corrupted files recovered. Only backups can do that.

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9 hours ago, davidst95 said:

Hi, I have four 10GB WDC Red HDDs.   Is it overkill to have two parity drives for just four drives?   I don't think I would need more than 20TB of space.   I will also be using two 500GB SSDs for cache.   Thanks!

 

David

Your statement is a little confusing. It can mean 2 things:

  1. 2x data drives + 2x parity drives = 4x 10TB that you have.
  2. 4x 10TB data drives + 2x parity drives (to be purchased)

If it's (1) then you are better off with a single parity and use the other drive as a backup for your most critical data.

If you already have a backup solution in place then 3x array + 1x parity should be sufficient.

 

If it's (2) then it's less clearcut.

Based on backblaze HDD failure stat, I estimated that the "reasonable break-even point" (defined by me as when the expected rate of failure is not higher than the number of parity) for a dual-parity is still higher than 6 drives (i.e. 4 data, 2 parity). It is even higher if we only consider stat for only 8TB+ drives - which even Backblaze observed that they didn't seem to fail as often.

However, I can see merit of dual parity for the very risk-averse - after all HDD failure is a probability thing.

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8 hours ago, testdasi said:

Your statement is a little confusing. It can mean 2 things:

  1. 2x data drives + 2x parity drives = 4x 10TB that you have.
  2. 4x 10TB data drives + 2x parity drives (to be purchased)

If it's (1) then you are better off with a single parity and use the other drive as a backup for your most critical data.

If you already have a backup solution in place then 3x array + 1x parity should be sufficient.

 

If it's (2) then it's less clearcut.

Based on backblaze HDD failure stat, I estimated that the "reasonable break-even point" (defined by me as when the expected rate of failure is not higher than the number of parity) for a dual-parity is still higher than 6 drives (i.e. 4 data, 2 parity). It is even higher if we only consider stat for only 8TB+ drives - which even Backblaze observed that they didn't seem to fail as often.

However, I can see merit of dual parity for the very risk-averse - after all HDD failure is a probability thing.

Thanks for the reply and information.  I have a total of 4x10tb drives.  If I want to use the 4 drive as a backup should I add to unraid as an unassigned drive and use or write a script to transfer important data over? Thanks again! 

 

David 

 

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44 minutes ago, davidst95 said:

Thanks for the reply and information.  I have a total of 4x10tb drives.  If I want to use the fourth drive as a backup should I add to unraid as an unassigned drive and use or write a script to transfer important data over? Thanks again! 

 

David 

 

 

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