[ovirt-users] strange iscsi issue

[Karli Sjöberg]

tis 2015-09-08 klockan 06:59 +0200 skrev Demeter Tibor:
> Hi,
> Thank you for your reply.
> I'm sorry but I don't think so. This storage is fast, because it is a SSD based storage, and I can read/write to it with fast performance.
> I know, in virtual environment the I/O always slowest than on physical, but here I have a very large difference. 
> Also, I use ext4 FS.

My suggestion would be to use a filesystem benchmarking tool like bonnie
++ to first test the performance locally on the storage server and then
redo the same test inside of a virtual machine. Also make sure the VM is
using VirtIO disk (either block or SCSI) for best performance. I have
tested speeds over 1Gb/s with bonded 1Gb NICS so I know it should work
in theory as well as practice.

Oh, and for the record. IO doesn´t have to be bound by the speed of
storage, if the host caches in RAM before sending it over the wire. But
that in my opinion is dangerous and as far as I know, it´s not actived
in oVirt, please correct me if I´m wrong.

/K

> 
> Thanks
> 
> Tibor
> 
> 
> ----- 2015. szept.. 8., 0:40, Alex McWhirter alexmcwhirter at triadic.us írta:
> 
> > 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
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