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Slow parity check after adding new disks

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I recently added some disks to my array, and now my parity check is impossibly slow. I'm seeing speeds of 170-225Kbps, with a time to completion time of 360-780 days. I suspected issues with the new disks or controller, however DiskSpeed seems normal across all disks (attached). The array was setup with 4x 16TB SATA disks, 1 for parity and the 3 others for data. I added 8x 10TB SAS disks via a LSI 933-8i. What else can I look at that may be causing the parity check issue?

Screenshot 2026-04-07 130213.png

Solved by JorgeB

  • Community Expert

There are ATA errors with multiple disks: disk 1, disk 2, and disk3. Anything in common, like a power/splitter? Check/replace cables and try again.

  • Author
3 minutes ago, JorgeB said:

There are ATA errors with multiple disks: disk 1, disk 2, and disk3. Anything in common, like a power/splitter? Check/replace cables and try again.

Those are my 3 original disks in the array, that have actual data on them (new ones don't yet). They are all on a power splitter, yes. As well, they're on the mobo SATA controller.

Edited by jamesmcg
Added note for SATA controller.

  • Community Expert
  • Solution
23 minutes ago, jamesmcg said:

They are all on a power splitter, yes.

If this is a SATA to SATA splitter, it should never split one into more than two, Molex is OK, but it's also good to avoid them whenever possible, but check/replace that to start with.

  • Author

I've removed the 8 disks I added last week, which were still empty. Now my parity check is looking WAY better:

Total size:

16 TB

Elapsed time:

9 minutes

Current position:

99.7 GB (0.6 %)

Estimated speed:

268.6 MB/sec

Estimated finish:

I have some more cables on order, so I can go direct from the PSU to the disks. It's a modular PSU I yanked from an old gamin PC, missing all extra cables. Lesson learned for me!

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