General Rule For The Number Of Parity Disks?

[Badboy]

Hi everybody,

I have (4 - 10 TB) drives and (1 - 10 TB ) parity drive. I'm just curious, at what point or number of drives should I consider having a second parity drive? I know I'm a ways off from worrying about that just yet. Is there a general rule?

 

Edited November 13, 2019 by Badboy

[JorgeB]

There's no general rule, depends on a number of things:

 

-how many disks

-size of the disks

-how important is the data

-existence of backups

 

I generaly have single parity on servers with up to 8 disks, dual parity for with more than 8 disks, but I have at least one full backup of every server.

[Badboy]

7 minutes ago, johnnie.black said:

There's no general rule, depends on a number of things:

 

-how many disks

-size of the disks

-how important is the data

-existence of backups

 

I generaly have single parity on servers with up to 8 disks, dual parity for with more than 8 disks, but I have at least one full backup of every server.

Hi Johnnie,

Let's just say these 4 10TB drives are full and the data is important.  As of right now would this one parity drive be ok? I do backup most of this data on a small Qnap and additional desktop drives.  At some point I'm going to move the backup drives to the Unraid server, I want to consolidate everything into one for better transfer speeds and save on power.  I use a Thermaltake case which can house 20 drives.

[JorgeB]

If you have backups of at least most of it I would say 1 parity is OK for now, but with such high capacity disks I would go for dual parity at around 6 data disks.

[itimpi]

It is important that you continue to keep backups of important data regardless of the number of parity disks.   Parity protects against disk failure, but it does not protect against other potential causes of data loss.

[JonathanM]

20 minutes ago, Badboy said:

At some point I'm going to move the backup drives to the Unraid server, I want to consolidate everything into one for better transfer speeds and save on power.

That's not an ideal move. If you have an incident that takes out multiple drives, you could easily lose both the primary data and all your backups.

[JorgeB]

At some point I'm going to move the backup drives to the Unraid server, I want to consolidate everything into one for better transfer speeds and save on power.

That's not an ideal move. If you have an incident that takes out multiple drives, you could easily lose both the primary data and all your backups.

Yes, I missed that part of your post, dual parity adds redundancy, it's not a substitute for backups, you're much better off with single parity and backups than dual parity and no backups, I was recommending dual parity with 6+ plus disks + backups.

 

 

[Badboy]

Not going to attach those drives to the raid. Going to add them as unassigned  devices.

[JorgeB]

10 minutes ago, Badboy said:

Not going to attach those drives to the raid. Going to add them as unassigned  devices.

It's fine if you disconnect them when not in use, or e.g. a PSU problem can fry all the drives connected.

[Badboy]

7 minutes ago, johnnie.black said:

It's fine if you disconnect them when not in use, or e.g. a PSU problem can fry all the drives connected.

That's a very good point!!! Didn't think about that. I shut my Qnap down after backups because I don't use it for anything anyway. I will just have to remember to disconnect when finished with the backups. Thanks for the feedback, appreciate it.

[Badboy]

21 minutes ago, Badboy said:

That's a very good point!!! Didn't think about that. I shut my Qnap down after backups because I don't use it for anything anyway. I will just have to remember to disconnect when finished with the backups. Thanks for the feedback, appreciate it.

With the number of drives you have, do you spin them down when not in use?  I never have, my thought it is more wear an tear on starting them backup.  Even my desktops I never shut them down, might put them into sleep mode.