Rebuilding/Adding Drives to the pool

[techguru6966]

Good morning all!

 

I deal with various types of arrays in my line of work, mostly ZFS arrays and pools.  With the particular XFS pool Unraid is using, can someone explain why my array needs to be down while it rebuilds a drive? With ZFS I can add a drive to a pool and it will resilver while the pool is up. With Unraid my entire pool has to be down while it rebuilds a drive which is really a damper because it can days with the 10-16TB drives I add.  

 

Am I doing something wrong or is that just the nature of this pool?

 

I apologize in advance if this was asked previously. I did try searching the forums, but did not see this particular question asked.

 

Thank you!!

[itimpi]

21 minutes ago, techguru6966 said:

Good morning all!

 

I deal with various types of arrays in my line of work, mostly ZFS arrays and pools.  With the particular XFS pool Unraid is using, can someone explain why my array needs to be down while it rebuilds a drive? With ZFS I can add a drive to a pool and it will resilver while the pool is up. With Unraid my entire pool has to be down while it rebuilds a drive which is really a damper because it can days with the 10-16TB drives I add.  

 

Am I doing something wrong or is that just the nature of this pool?

 

I apologize in advance if this was asked previously. I did try searching the forums, but did not see this particular question asked.

 

Thank you!!

 

Assuming you are talking about the main Unraid array, then array does NOT need to be down while it is rebuilding a data drive or building a parity drive contents.    It will only be down if you do the operation in Maintenance mode.   If however you have the array available while either parity or a data drive is being built then any read/write operations to the array badly degrade each others performance while they are both running, but as long as you are aware of this and the amount of read/write to data drives will be minimal this is normally an acceptable compromise.   Note these statements apply to the main Unraid array which is not limited to XFS as drives can also be in BTRFS and XFS and they can be mixed - it is just in the main Unraid array each drive is a free-standing file system.

 

There is an exception to this statement in what is called the Parity Swap procedure where you are trying to simultaneously upgrade a parity drive to a larger one, and then use the old parity drive to replace a (possible failed) drive in the main array.   In this case the array is not available during the initial phase while the old parity drive content are copied to the new larger parity drive, but it IS available at the second phase where the array drive that is being replaced is having it contents rebuilt.

 

[techguru6966]

6 hours ago, itimpi said:

 

Assuming you are talking about the main Unraid array, then array does NOT need to be down while it is rebuilding a data drive or building a parity drive contents.    It will only be down if you do the operation in Maintenance mode.   If however you have the array available while either parity or a data drive is being built then any read/write operations to the array badly degrade each others performance while they are both running, but as long as you are aware of this and the amount of read/write to data drives will be minimal this is normally an acceptable compromise.   Note these statements apply to the main Unraid array which is not limited to XFS as drives can also be in BTRFS and XFS and they can be mixed - it is just in the main Unraid array each drive is a free-standing file system.

 

There is an exception to this statement in what is called the Parity Swap procedure where you are trying to simultaneously upgrade a parity drive to a larger one, and then use the old parity drive to replace a (possible failed) drive in the main array.   In this case the array is not available during the initial phase while the old parity drive content are copied to the new larger parity drive, but it IS available at the second phase where the array drive that is being replaced is having it contents rebuilt.

 

Thank you very much for this response.  This explains why the array was down while rebuilding parity. 

 

Can you tell me, if I add another parity drive will it also be down for as long while in the first phase?

[itimpi]

When you add a parity drive the array does not need to be down while you are building parity - it is only in the special case of using the parity swap procedure which does not apply in this scenario that there is some forced array downtime.    Performance is, however, severely degraded if you try to do anything with the array at the same time.

[techguru6966]

Thank you very much for the information.  I'll mark this as resolved.