[ovirt-users] strange iscsi issue

[Alex McWhirter]

Unless you're using a caching filesystem like zfs, then you're going to be limited by how fast your storage back end can actually right to disk. Unless you have a quite large storage back end, 10gbe is probably faster than your disks can read and write.

On Sep 7, 2015 4:26 PM, Demeter Tibor <tdemeter at itsmart.hu> wrote:
>
> Hi All,
>
> I have to create a test environment for testing purposes, because we need to testing our new 10gbe infrastructure.
> One server that have a 10gbe nic - this is the vdsm host and ovirt portal.
> One server that have a 10gbe nic - this is the storage.
>
> Its connected to each other throught a dlink 10gbe switch.
>
> Everything good and nice, the server can connect to storage, I can make and run VMs, but the storage performance from inside VM seems to be 1Gb/sec only. 
> I did try the iperf command for testing connections beetwen servers, and it was 9.40 GB/sec. I have try to use hdparm -tT /dev/mapper/iscsidevice and also it was 400-450 MB/sec. I've got same result on storage server.
>
> So:
>
> - hdparm test on local storage ~ 400 mb/sec
> - hdparm test on ovirt node server through attached iscsi device ~ 400 Mb/sec
> - hdparm test from inside vm on local virtual disk - 93-102 Mb /sec
>
> The question is : Why?
>
> ps. I Have only one ovirtmgmt device, so there are no other networks. The router is only 1gbe/sec, but i've tested and the traffic does not going through  this.
>
> Thanks in advance,
>
> Regards, 
> Tibor