High read IOPS with file backend

[Crowder, Travis]

Can you publish your testing methods and configurations for both Varnish
and Nginx?  Can you include the Network graphs and/or the Connections
graphs for Varnish and Nginx?

-Travis

On 8/16/13 12:29 PM, "Bryan Stillwell" <bstillwell at photobucket.com> wrote:

>I'm looking at converting all of our nginx caching servers over to
>varnish, but I'm seeing some oddities with the 'file' storage backend
>that I'm hoping someone could shed some light on.
>
>Hardware specs for both machines:
>
>Dell PowerEdge R610
>  Dual Xeon E5620 @ 2.40GHz
>  64GiB memory
>  4x 240GB SSDs in a RAID5 attached to a PERC H700 RAID controller
>
>The following image compares CPU, memory, and IOPS for both a machine
>running varnish (left), and one running nginx (right):
>
>http://i1217.photobucket.com/albums/dd391/bstillwell_pb/Graphs/varnish-vs-
>nginx.png
>
>At the most recent sample, each machine was handling ~350 requests/sec.
>
>As you can see the varnish machine has a lot more CPU time dedicated to
>I/O wait, which matches up with ~5x higher IOPS numbers.  However, the
>biggest difference is that varnish is using ~25x more read IOPS than
>nginx.
>
>As for the jumps in the IOPS graph, I believe they can be explained by:
>
>Wednesday @ 10:00a: Started taking traffic
>Wednesday @ 11:00a: Memory cache filled, started using SSDs
>Wednesday @  4:00p: TTL of 6 hours was hit, objects start expiring
>Wednesday @  7:15p: SSD cache filled
>
>I pre-allocated the storage with fallocate (fallocate -l 450g
>/cache/varnish_storage.bin) to make sure that wasn't helping contribute
>to the issue.
>
>Any ideas on what could be tuned to reduce the number of read IOPS to be
>more inline with nginx?
>
>Thanks,
>Bryan
>
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