changing priority of the disk reconstruction

[xuanchel]

Hello,

I got a question from customer and don't know how to explain it. Is there any document or idea to answer this question?

Question:

what if there is a situation like the disk reconstruction is being proceed  and this process give an impact to the performance of foreground I/O.

Will foreground I/O get less performance impact if changing value of raid.reconstruct.perf_impact  to low during disk reconstruction? Or the change will be reflected in the disk reconstruction.

cluster1::> storage raid-options modify -node * -name raid.reconstruct.perf_impact -value low

[akiendl]

ONTAP does automatically make sure that a reconstruct has no impact. In the incredibly rare events it has you can use the option but I have not seen it needed in years.

[xuanchel]

Customer know the reconstruction have no impact but they still want to know if changing the value of the   raid.reconstruct.perf_impact to low will directly reflect to the disk reconstruction that is being proceed.

[DarrenJ]

Check this KB.

https://kb.netapp.com/Advice_and_Troubleshooting/Data_Storage_Software/ONTAP_OS/How_to_increase_priority_for_disk_reconstruction

Low

• The storage system uses very little of the system resources.
• This setting lightly affects storage system performance.
• Reconstruction takes longer to complete, increasing the time that the storage system is running in degraded mode.

In short, setting it to low will slow down reconstruction.  

[paul_stejskal]

I've never got a conclusive answer but I've heard that in newer versions of ONTAP this was fixed. In older versions it was a RFE to be dynamic during a disk reconstruct but never got any traction.

[JonathanGaudette]

Low=less impact to frontend clients (and slower reconstruct speed)