Re: prioritizing reads over writes

["Xu (Simon) Chen" <xchenum@xxxxxxxxx>]

I am already using deadline scheduler, with the default parameters:

read_expire=500

write_expire=5000

writes_starved=2

front_merges=1

fifo_batch=16

I remember tuning them before, didn't make a great difference.

-Simon

On Fri, Oct 31, 2014 at 3:43 PM, Nick Fisk <nick@xxxxxxxxxx> wrote:

Hi Simon,

 

Have you tried using the Deadline scheduler on the Linux nodes? The deadline scheduler prioritises reads over writes. I believe it tries to service all reads within 500ms whilst writes can be delayed up to 5s.

 

I don’t the exact effect Ceph will have over the top of this, but this would be the first thing I would try.

 

Nick

 

From: ceph-users [mailto:ceph-users-bounces@xxxxxxxxxxxxxx] On Behalf Of Xu (Simon) Chen
Sent: 31 October 2014 19:37
To: ceph-users@xxxxxxxxxxxxxx
Subject: prioritizing reads over writes

 

Hi all,

 

My workload is mostly writes, but when the writes reach a certain throughput (iops wise not much higher) the read throughput would tank. This seems to be impacting my VMs' responsiveness overall. Reads would recover after write throughput drops.

 

Is there any way to prioritize read over write, or at least guarantee a certain level of aggregated read throughput in a cluster?

 

Thanks.

-Simon

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