Volume schedule during peak usage

Question

Running OS 6.10.1.&nbsp;&nbsp;My scrub runs 3 times a year and it takes about a week to finish. Is it possible to schedule it so that the scrub uses less CPU during peak usage and runs full bore at night when nobody is using it?&nbsp;

StephenB · Answer

vrspectre&nbsp;wrote:
&nbsp;
Do you know how i might pause it and resume it? would love to schedule it.&nbsp;

I don't know exactly what command is being used for the mdadm piece, and that would matter for this. mdgm&nbsp;might know.
&nbsp;
For the btrfs piece of it, you'd enter&nbsp;
# btrfs scrub cancel /path
to pause, and then later on use
# btrfs scrub resume /path
to resume it.&nbsp; The status is saved in a file, and it will pick up from where it left off.
&nbsp;
You can see the status using&nbsp;
# btrfs scrub status -d /path

&nbsp;
&nbsp;
&nbsp;

Sandshark · Answer

As best as I can tell, the MDADM re-sync is triggered by the equivalent&nbsp;of&nbsp;echo repair &gt; /sys/block/mdXXX/md/sync_action&nbsp;(where XXX is the array&nbsp;designator, 127 for most single-array NAS).&nbsp; You should be able to pause it with echo 0 &gt;/proc/sys/dev/raid/speed_limit_max. or slow it way down with something between the default of 200000 and 0.&nbsp; Other methods I know of will cause it to start from scratch when re-started, not resume where it left off.&nbsp;I have long complained that Netgear is needlessly stressing the drives and taking up valuable assets by doing both btrfs scrub and mdadm re-sync simultaneously.&nbsp; My personal experience by doing each manually shows the total time for doing them separately is about the same as concurrently since each slows the other when they are concurrent.&nbsp; They should be automatically sequential or two separate scheduled operations.&nbsp; My only guess is that the only way to easily show the total progress is to actually only look at one of the processes as it is affected by the other.&nbsp; In other words, lazy programming.&nbsp;While the processes do take 100% of the CPU on a system like a 516, that's only when others aren't asking for time.&nbsp; It's a bigger deal on less powerful NAS.&nbsp; And the drive I/O is a huge problem with an EDA500 on any NAS.&nbsp; When I had a 516 with two EDA500's, a scrub&nbsp;could backlog other processes needing access to the array in one of the EDA's that the whole NAS nearly locked up and the sync/scrub slowed to such a crawl (having&nbsp;already been slow with the eSATA port expansion interface), that I never even found out if it would ever come out of it.&nbsp; I ultimately just did each manually via SSH, though I suppose I could have created a CRON process to do it periodically.&nbsp; I moved to a rack-mount NAS instead.

StephenB · Answer

vrspectre&nbsp;wrote:
Running OS 6.10.1.&nbsp;
&nbsp;
My scrub runs 3 times a year and it takes about a week to finish. Is it possible to schedule it so that the scrub uses less CPU during peak usage and runs full bore at night when nobody is using it?&nbsp;

It already is running at a background priority.&nbsp; FWIW, I believe the performance impact is largely due to the continuous disk I/O.&nbsp; I don't think CPU would be a major factor on an RN516 (which is what I think you have???).
&nbsp;
It is possible to run the commands via ssh. There is a way to pause/resume the BTRFS scrub. Pausing mdadm checkarray is supposed to be possible, but I've never tried it.&nbsp; &nbsp;

vrspectre · Answer

One of the apps I have has a CPU usage which shows 100% cpu being used. I supposed I/O is probably also a bottle neck. basically i just want it to run at night and pause during the day.

Do you know how i might pause it and resume it? would love to schedule it.

StephenB · Answer

Sandshark&nbsp;wrote:
As best as I can tell, the MDADM re-sync is triggered by the equivalent&nbsp;of&nbsp;echo repair &gt; /sys/block/mdXXX/md/sync_action&nbsp;(where XXX is the array&nbsp;designator, 127 for most single-array NAS).&nbsp; You should be able to pause it with echo 0 &gt;/proc/sys/dev/raid/speed_limit_max. or slow it way down with something between the default of 200000 and 0.&nbsp; Other methods I know of will cause it to start from scratch when re-started, not resume where it left off.

Thx for sharing this.
&nbsp;
Sandshark&nbsp;wrote:
&nbsp;
While the processes do take 100% of the CPU on a system like a 516, that's only when others aren't asking for time.&nbsp; &nbsp;

That of course makes sense, since the process is running in the background. I agree that the disk I/O is a bigger concern.
&nbsp;
FWIW, I just let it run on schedule in my 526x, and haven't observed an objectionable performance drop (even with the disk trashing).&nbsp; My RN202 has two jbod volumes, so the btrfs scrub part is the only thing that actually takes time/resources there.
&nbsp;
Sandshark&nbsp;wrote:
&nbsp;
I have long complained that Netgear is needlessly stressing the drives and taking up valuable assets by doing both btrfs scrub and mdadm re-sync simultaneously.

&nbsp;I'd rather be able to run the RAID resync and BTRFS scrub independently - even setting aside the resources needed.&nbsp; They do two very different things.

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Volume schedule during peak usage

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