----- Original Message -----> From: "Lindsay Mathieson" <lindsay.mathieson at gmail.com>
> To: "gluster-users" <gluster-users at gluster.org>
> Sent: Monday, November 3, 2014 12:41:59 AM
> Subject: [Gluster-users] iowait issues
>
> Using glusterfs (2 nodes, one disk each, replicated) to serve up my
> kvm disk images. Wehn 4+ vm's are running, I'm seeing iowait upto
25%,
> which is causing problems.
>
> Oddly my nas, which has crappy network performance compared to the
> gluster cluster doesn't display this problem, but it does use a RAID10
> array.
>
> Would my iowait problems because by the gluster network replication or
> by the single disks (WD Red 3TB).
>
> If the latter, would adding a ssd cache help? something else?
What is you NW bandwidth? If you are using gigabit then I can see this as the
problem. I have found that without at very least 20 MB / sec of throughput per
VM they get difficult to use with a GUI. So with gigabit and replication:
Gigabit = 120 MB / sec, divide that by 2 for replication:
60 MB / sec / 4 VMs = 15 MB / sec per VM
That is under the at least 20 that I like to see. With gluster you are using
1/2 you bandwidth for replication and with the NAS you are probably getting the
full gigabit. Also having the RAID on the NAS defiantly helps, but I think in
this case you are probably hitting the NIC as the bottleneck. I would look at
NW bandwith first and then look at RAID, you need to have a fast enough back end
to service the bandwidth of your NICs. Also the more spindles you have the
better IOPS / smallfile / random IO will be. What about 10G NW cards or NIC
bonding? How many VMs are you looking to run? What sort of workload?
-b
> thanks,
>
> --
> Lindsay
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