Re: Gluster 3.5.2 gluster, how does cache work?

[Pranith Kumar Karampuri <pkarampu@xxxxxxxxxx>]

CC Raghavendra G, who maintains performance translators to explain how io-cache works.

Pranith

On 08/22/2014 09:14 PM, Juan José Pavlik Salles wrote:

Hi Ben, I also thought of that, but look at this:

[root@gluster-client-1 gluster_vol]# echo 3 > /proc/sys/vm/drop_caches; dd if=/mnt/gluster_vol/128 of=/dev/null bs=1M; 

128+0 records in

128+0 records out

134217728 bytes (134 MB) copied, 6,70874 s, 20,0 MB/s

[root@gluster-client-1 gluster_vol]# echo 3 > /proc/sys/vm/drop_caches; dd if=/mnt/gluster_vol/128 of=/dev/null bs=1M; 

128+0 records in

128+0 records out

134217728 bytes (134 MB) copied, 0,160485 s, 836 MB/s

[root@gluster-client-1 gluster_vol]# echo 3 > /proc/sys/vm/drop_caches; dd if=/mnt/gluster_vol/128 of=/dev/null bs=1M; 

128+0 records in

128+0 records out

134217728 bytes (134 MB) copied, 0,148219 s, 906 MB/s

[root@gluster-client-1 gluster_vol]# 

even dropping kernel caches I get a really fast answer. I think that this is io-cache translator working on the client side for sure.

2014-08-22 12:27 GMT-03:00 Ben Turner <bturner@xxxxxxxxxx>:

----- Original Message -----
> From: "Juan José Pavlik Salles" <jjpavlik@xxxxxxxxx>
> To: gluster-users@xxxxxxxxxxx
> Sent: Thursday, August 21, 2014 4:07:28 PM
> Subject: Gluster 3.5.2 gluster, how does cache work?
>
> Hi guys, I've been reading a bit about caching in gluster volumes, but I
> still don't get a few things. I set up a gluster replica 2 volume like this:
>
> [root@gluster-test-1 ~]# gluster vol info vol_rep
> Volume Name: vol_rep
> Type: Replicate
> Volume ID: b77db06d-2686-46c7-951f-e43bde21d8ec
> Status: Started
> Number of Bricks: 1 x 2 = 2
> Transport-type: tcp
> Bricks:
> Brick1: gluster-test-1:/ladrillos/l1/l
> Brick2: gluster-test-2:/ladrillos/l1/l
> Options Reconfigured:
> performance.cache-min-file-size: 90MB
> performance.cache-max-file-size: 256MB
> performance.cache-refresh-timeout: 60
> performance.cache-size: 256MB
> [root@gluster-test-1 ~]#
>
> Then I mounted the volume with gluster client on another machine. I created
> an 80Mbytes file called 80, and here you have the reading test:
>
> [root@gluster-client-1 gluster_vol]# dd if=/mnt/gluster_vol/80 of=/dev/null
> bs=1M
> 80+0 records in
> 80+0 records out
> 83886080 bytes (84 MB) copied, 1,34145 s, 62,5 MB/s
> [root@gluster-client-1 gluster_vol]# dd if=/mnt/gluster_vol/80 of=/dev/null
> bs=1M
> 80+0 records in
> 80+0 records out
> 83886080 bytes (84 MB) copied, 0,0246918 s, 3,4 GB/s
> [root@gluster-client-1 gluster_vol]# dd if=/mnt/gluster_vol/80 of=/dev/null
> bs=1M
> 80+0 records in
> 80+0 records out
> 83886080 bytes (84 MB) copied, 0,0195678 s, 4,3 GB/s
> [root@gluster-client-1 gluster_vol]#

You are seeing the effect of client side kernel caching.  If you want to see the actual throughput for reads run:

sync; echo 3 > /proc/sys/vm/drop_caches; dd blah

Kernel caching happens on both the client and server side, when I want to see uncached performance I drop caches on both clients and servers:

run_drop_cache()
{
    for host in $MASTERNODE $NODE $CLIENT
    do
        ssh -i /root/.ssh/my_id root@${host} echo "Dropping cache on $host"
        ssh -i /root/.ssh/my_id root@${host} sync
        ssh -i /root/.ssh/my_id root@${host} "echo 3 > /proc/sys/vm/drop_caches"
    done
}

HTH!

-b

> Cache is working flawlessly, (even though that 80 Mbytes is smaller than the
> min-file-size value, but I don't care about it right now) what I don't get
> is where cache is being stored. Is it stored on the client side or on the
> server side? According to documentation, the io-cache translator could be
> loaded on both sides (client and server), how can I know where it is being
> loeaded? It looks like as it was being stored locally because of the speed,
> but I'd like to be sure.
>
> Thanks!
>
> --
> Pavlik Salles Juan José
> Blog - http://viviendolared.blogspot.com
>

> _______________________________________________
> Gluster-users mailing list
> Gluster-users@xxxxxxxxxxx
> http://supercolony.gluster.org/mailman/listinfo/gluster-users

--

Pavlik Salles Juan José

Blog - http://viviendolared.blogspot.com

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