Parity/main drive swap/upgrade question

[Jake Lowe]

Here is my current unraid setup. I want to add a 1tb drive to my array. I was going to move one of my 500g parity drive to my main array and then add the 1tb drive to the parity slot I just switched out. Is this how I should do this or should I only have one parity drive?

I WANT TO HAVE ALL MY DATA PROTECTED IN CASE OF A DRIVE FAIL.

IF I SETUP MY ARRAY WILL ALL DATA BE PROTECTED?

[John_M]

It seems more logical to me to replace one of the parity disks with the 1 TB drive first, then add the old drive as a new data disk when the parity has rebuilt.

 

Your method would work but it's less safe as you're needlessly trashing the contents of a parity disk before you actually have to.

 

Edited November 26, 2018 by John_M
Improved grammar

[Jake Lowe]

OK. Thanks

[trurl]

Personally I wouldn't bother with dual parity with so few disks.

[Jake Lowe]

1 hour ago, trurl said:

Personally I wouldn't bother with dual parity with so few disks.

If I have a 1tb drive as parity and 1320gb as my main data not all of my data will be protected, correct?

[JonathanM]

10 minutes ago, Jake Lowe said:

If I have a 1tb drive as parity and 1320gb as my main data not all of my data will be protected, correct?

Unraid won't let you have a parity drive smaller than any data drive.

 

Parity doesn't store any data by itself, it works along with all the other remaining drives to reconstruct 1 missing drive.

[itimpi]

10 minutes ago, Jake Lowe said:

If I have a 1tb drive as parity and 1320gb as my main data not all of my data will be protected, correct?

All your data IS protected!    When a drive fails it is reconstructed using the combination of the parity drive plus ALL the other data drives.

you might want to read the Wiki to understand how parity works.

[Jake Lowe]

1 minute ago, itimpi said:

All your data IS protected!    When a drive fails it is reconstructed using the combination of the parity drive plus ALL the other data drives.

you might want to read the Wiki to understand how parity works.

Ok. This is all very confusing to me.

I just want to make sure that all data is safe and happy with the new parity.

As long as it is I am going to continue with this new config.

One more question. How does another parity drive help protect data more? 

 

Sorry for all the questions. I am not very familiar with this mode of backup/data protection.

[trurl]

 

26 minutes ago, Jake Lowe said:

If I have a 1tb drive as parity and 1320gb as my main data not all of my data will be protected, correct?

No, you have 2 x 500GB parity, which gives you 2 independent 500GB parity disks. You don't add them together.

 

A single 500GB parity disk can protected any number of data disks, as long as each data disk is 500GB or less.

 

Parity IS NOT a backup. As mentioned, parity allows the data for a missing disk to be calculated from the parity disk PLUS ALL the other disks.

 

Take a look at this wiki and see if you can understand how parity works.

 

https://wiki.unraid.net/UnRAID_6/Overview#Parity-Protected_Array

 

It really isn't that complicated. And it isn't very different from other systems like the various RAIDs that also use parity.

 

[itimpi]

It is worth pointing out that the 2nd parity disk works in a similar way to that described for parity1 in the suggested link but uses a different mathematical formula so that parity2 is independent of parity1.

[Jake Lowe]

51 minutes ago, itimpi said:

It is worth pointing out that the 2nd parity disk works in a similar way to that described for parity1 in the suggested link but uses a different mathematical formula so that parity2 is independent of parity1.

Ok. Thanks, everyone for your input. I really appreciate it. I am going to remove all parity drives and install a 1tb drive. I will move the parity drives to the main array. Thanks, everyone for your input! Let me know if I made a stupid mistake in what I just said I am going to do

 

[itimpi]

1 minute ago, Jake Lowe said:

Ok. Thanks, everyone for your input. I really appreciate it. I am going to remove all parity drives and install a 1tb drive. I will move the parity drives to the main array. Thanks, everyone for your input! Let me know if I made a stupid mistake in what I just said I am going to do

 

Is that 1TB drive going to become a new parity1 drive?    If so that would be OK.   If not then your array would be unprotected against drive failure.   It is perfectly OK to run unprotected if you have a backup strategy in place to recover data if a drive fails, but most people prefer to have at least one level of parity protection in place.

[Jake Lowe]

1 minute ago, itimpi said:

Is that 1TB drive going to become a new parity1 drive?    If so that would be OK.   If not then your array would be unprotected against drive failure.   It is perfectly OK to run unprotected if you have a backup strategy in place to recover data if a drive fails, but most people prefer to have at least one level of parity protection in place.

I am going to have one 1tb drive for parity. Just to make sure if one drive fails on the array all data on that drive will be rebuilt, correct?

[itimpi]

9 minutes ago, Jake Lowe said:

I am going to have one 1tb drive for parity. Just to make sure if one drive fails on the array all data on that drive will be rebuilt, correct?

Yes.  The number of simultaneous array drive failures that can be handled is the same as the number of parity drives.

 

If you DO happen to get a drive failure and are not sure how to proceed then ask here in the forum first.    Taking the right action will recover your data, but taking the wrong action can result in data loss.  One is often in 'panic' mode after a drive failure and prone to rushing things.

 

It is worth pointing out that you should still have a backup strategy in place for any data you really cannot afford to lose.   Although unlikely it is possible that some catastrophic event (e.g. PSU going rogue, lightning strike) could fail multiple drives simultaneously and the simple recovery process will not work.   Unraid is good at handling even such events if one is careful but you do not want to rely on this being the case.

Edited November 27, 2018 by itimpi

[Jake Lowe]

2 minutes ago, itimpi said:

Yes.  The number of simultaneous array drive failures that can be handled is the same as the number of parity drives.

 

If you DO happen to get a drive failure and are not sure how to proceed then ask here in the forum first.    Taking the write action will recover your data, but taking the wrong action can result in data loss.

 

It is worth pointing out that you should still have a backup strategy in place for any data you really cannot afford to lose.   Although unlikely it is possible that some catastrophic event (e.g. PSU going rogue, lightning strike) could fail multiple drives simultaneously and the simple recovery process will not work.   Unraid is good at handling even such events if one is careful but you do not want to rely on this being the case.

Ok. Thanks so much!

[trurl]

2 hours ago, Jake Lowe said:

I will move the parity drives to the main array.

Just to clear up some terminology for you. The parity drive(s) plus the assigned data disks ARE the array. In other words, parity is in the array by definition. If you notice in your screenshot the heading above parity and those assigned data disks it says "Array Devices".

 

Flash, cache disks and any unassigned disks are not in the array.

[Jake Lowe]

3 minutes ago, trurl said:

Just to clear up some terminology for you. The parity drive(s) plus the assigned data disks ARE the array. In other words, parity is in the array by definition. If you notice in your screenshot the heading above parity and those assigned data disks it says "Array Devices".

 

Flash, cache disks and any unassigned disks are not in the array.

Yes, I know. Sorry, my bad - bad wording