Re: Slow recovery on Quincy

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On 17/05/2023 03.07, 胡 玮文 wrote:
> Hi Sake,
> 
> We are experiencing the same. I set “osd_mclock_cost_per_byte_usec_hdd” to 0.1 (default is 2.6) and get about 15 times backfill speed, without significant affect client IO. This parameter seems calculated wrongly, from the description 5e-3 should be a reasonable value for HDD (corresponding to 200MB/s). I noticed this default is originally 5.2, then changed to 2.6 to increase the recovery speed. So I suspect the original author just convert the unit wrongly, he may want 5.2e-3 but wrote 5.2 in code.
> 
> But all this may be not important in the next version. I see the relevant code is rewritten, and this parameter is now removed.
> 
> high_recovery_ops profile works very poorly for us. It increase the average latency of client IO from 50ms to about 1s.
> 
> Weiwen Hu
> 

Thank you for this, that parameter indeed seems completely wrong
(assuming it means what it says on the tin). After changing that my
Quincy cluster is no recovering at a much more reasonable speed.

- Hector
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