Re: Poor read performance.

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On Wed, Apr 25, 2018 at 10:58:43PM +0000, Blair Bethwaite wrote:
:Hi Jon,
:
:On 25 April 2018 at 21:20, Jonathan Proulx <jon@xxxxxxxxxxxxx> wrote:
:>
:> here's a snap of 24hr graph form one server (others are similar in
:> general shape):
:>
:> https://snapshot.raintank.io/dashboard/snapshot/gB3FDPl7uRGWmL17NHNBCuWKGsXdiqlt
:
:That's what, a median IOPs of about 80? Pretty high for spinning disk.
:I'd guess you're seeing write-choking. You might be able to improve
:things a bit by upping your librbd cache size (though obviously that
:would only have an effect on new or reset instances), also perhaps
:double check your block queue scheduler max_sectors_kb inside a guest
:and make sure you're not splitting up all writes into 512 byte chunks.
:But does kinda look like you need more hardware, and fast.

Those block queue scheduler tips *might* help me squeeze a bit more
till next budget starts July 1...

Seeing yesterday I have 75% more VMs running than I thought does
change my perspective a bit make the "no we're really just crushed"
analysis more plausible!

Thanks,
-Jon


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