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Parity synchronization exhibiting sluggish and erratic speeds


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Hello,

 

I'm encountering a peculiar issue with my secondary unRAID server, which I'm utilizing for backup purposes. Most of the disks in use are repurposed drives, including 2 SMRs of 2TB capacity and a few CMRs (I think), around 500 GB each, originating from external hard drives. Despite these disks having satisfactory SMART reporting, I've noticed an anomaly during the parity sync process.

 

Typically, the disk speed for all drives should hover around 110 MB/s. However, during the parity sync, I've observed an irregular pattern: initially, the speed surges to 100 MB/s and maintains this rate for approximately 10 minutes. Subsequently, it drops to approximately 60 MB/s, and after a couple more minutes, it diminishes even further.

 

Interestingly, if I pause the parity sync for a brief period, say 5 minutes, and then resume it, the speed returns to the expected level.

 

What steps should I take to investigate this issue further?

 

Thank you!

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backup-diagnostics-20240326-1607.zip

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1 hour ago, StancuFlorin said:

surges to 100 MB/s and maintains this rate for approximately 10 minutes. Subsequently, it drops to approximately 60 MB/s, and after a couple more minutes, it diminishes even further.

This is typical with some SMR disks.

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2 minutes ago, StancuFlorin said:

From what I understood, it is recommended that at least the parity disks should be CMR, right? 

Yes.   SMR as parity disks is likely to sometimes lead to significant performance bottlenecks when copy large amounts of data.

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