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Forum Discussion
Performance during scrub
First off, yes I’ve definitely commented on this in the past. But this time I have context I didn’t have before. In particular, in the past week or so I have replaced three drives (due to increasing r...
At least part of the problem is that a scrub scheduled or manually invoked by the GUI performs a BTRFS scrub and an MDADM re-sync simultaneously, creating lots of drive I/O and thrashing. The situation is far worse on an EDA500 due to the eSATA interface adding an additional bottleneck. Scrubs alone initiated via SSH definately do not have as bad an impact (though they do have some).
While I can understand the need for both, I do not understand how anyone thinks that performing these two drive-intensive operations simultaneously is a reasonable approach. I do not know if the re-sync was added at some point, which would account for the difference in earlier OS versions.
My best guess as to why they are simulataneous: so that the OS need only look at the scrub progress provided by BTRFS (which typically ends last) for the displayed progress bar. That's not a good reason when the results are so bad.
I thought I disabled the scrub on both of my NAS devices, but apparently not :smileyfrustrated: My second NAS with the latest OS 6.10.2 has worked for 11 days now and getting from 86% to 88% took already more than 3 days. I pressed the cross besides the progress bar to stop the scrub. Is that Oke to do or can I have created a corruption by cancelling the scrub progress. The log shows that the scrub process was stopped so I guess all is fine. I just want to check to be sure and I do hope Netgear solves this as soon as possible.
Yes, that is perfectly fine. Some people never report problems with this, but I've never had a scrub go quickly... or normally.
The underlying issue seems to be that a "scrub" actually triggers a Btrfs scrub *and* an md sync at the same time. Awful. scrub should be scrub, period.
So, with ssh login I've done btrfs scrubs w/o issue, but those can't be scheduled. There may well be a reason they run them this way, but it's horribad for performance in at least some use cases.
I can't say I'm hopeful. It's come up many times over years and there has been no movement on it.
What I've taken to doing is running defrags, scrubs, and balances via SSH. In particular, I launch the scrub with
btrfs scrub start -c 3 /data
and check status with
btrfs scrub status /data
. Should you need/wish you may stop the operation safety by using
btrfs scrub cancel /data
Thank you btaroli it is a shame that this is not resolved whereas this appratnly is already know by Netgear for years. I have had a lot of issues with my RN628X's and I will reconsider when I replace them if I will stick with the ReadyNas series. The isuses I have had are:
- I have had a bricked RN628X during a firmware update;
- I have had a RN628X that all in a sudden without any notice or root cause got a read pnly volume;
- The RN628X I use as my main device is a lot of the times extremely slow without me understaindfing why (no apps installed and onlu opne activce user via a 1 Gigabit connection not doring anything particular). This sloweness is soo bad I had to abbandon the use of my only iSCSCI LUN that I was using as the disk was contantsly dropping off;
- This main RN628X now performing the regular disk check and whereas this was taking normally max 1 day it is now running for 5 days and I can's see a precentage of completion so I have not a clue if it got stalled or something. I will wait a couple of days more and then perform a reboot to see if that helps;
- This main RN628X has back-up jobs to my second RN628X and all jobs run fine except for one. Also here: I would not have a glue why this is.
All in all my trust in the RN628X is not what I want it to be. I do hope Netgear is reading the community messages and improving on this as I see a lot of room for improvement! I will use your steps to perfrom a scrub test. Do you by chance also have the commands I can use for a SSH session on defrag, balance and disk test as well?
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