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Changing 2 parity drives 1 at a time - rebuild speed seems limited compared to rebuilding a single drive data drive - WD180edgz-11blds0 - (SOLVED)

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Normally when i rebuild a drive it runs a bit slower until i get past the old 8gb seagate st8000dm004 drives which seem to limit me.  then the last 6tb would be fairly fast.  My old parity drives were 2 14TB Seagate (ST14000nm001g) which i believe were much faster..  Could this be my new WD parity drive doing the slowdown or is it a product of rebuilding 1 of 2 parity drives?  If so i think i should order some faster seagate drives for parity? 

Edited by FrozenGamer
solved

Solved by itimpi

  • Community Expert
  • Solution

Unless you have a very old CPU then doing 2 parity drives at the same time can run at a similar speed to doing a single one.   If the new parity drive is slower, that WILL slow things down as the speed is determined by the slowest drive at any point in the check.   I wonder if the new WD parity drive is using SMR technology rather than CMR as that could make a big difference .

  • Author

I don't know if it is CMR or not, i will see if i can find that out .. i hope not!

  • Community Expert
1 minute ago, FrozenGamer said:

I don't know if it is CMR or not, i will see if i can find that out .. i hope not!

CMR is fine - it is SMR that can be very slow once the drives internal buffer gets full.

  • Author

It is now just finishing the rebuild.. at 106 MB/S and started and stayed at about 57 MB/s..  Total time will have been 3 days 1.4 hrs, but i have 29 drives and really need to find a different caddy to store the drives with faster throughput i think.. eliminating the slower 8tb seagate smr drives will help. (3 more to get rid of) but those i think were just slow on the write and not so much on the read.. 3 days isn't a terrible overall time compared to my normal times though on the with 14tb seagate faster drives for parity, considering i am doing 4 more TB.

  • Community Expert
8 minutes ago, FrozenGamer said:

eliminating the slower 8tb seagate smr drives will help. (3 more to get rid of) but those i think were just slow on the write and not so much on the read.

Yes, SMR drives can slow down when writing but should read at normal speeds.   When there was a considerable price advantage to using SMR drive then it made sense with Unraid as it is most frequently used with media data that stays static once written so the write penalty was bearable.

  • FrozenGamer changed the title to Changing 2 parity drives 1 at a time - rebuild speed seems limited compared to rebuilding a single drive data drive - WD180edgz-11blds0 - (SOLVED)

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