[ovirt-users] VM has been paused due to storage I/O problem

[Gianluca Cecchi]

On Thu, Feb 2, 2017 at 12:09 PM, Yaniv Kaul <ykaul at redhat.com> wrote:

>
>
>
>>
>> I decided to switch to preallocated for further tests and confirm
>> So I created a snapshot and then a clone of the VM, changing allocation
>> policy of the disk to preallocated.
>> So far so good.
>>
>> Feb 2, 2017 10:40:23 AM VM ol65preallocated creation has been completed.
>> Feb 2, 2017 10:24:15 AM VM ol65preallocated creation was initiated by
>> admin at internal-authz.
>> Feb 2, 2017 10:22:31 AM Snapshot 'for cloning' creation for VM 'ol65' has
>> been completed.
>> Feb 2, 2017 10:22:31 AM Snapshot 'for cloning' creation for VM 'ol65' was
>> initiated by admin at internal-authz.
>>
>> so the throughput seems ok based on this storage type (the LUNs are on
>> RAID5 made with sata disks): 16 minutes to write 90Gb is about 96MBytes/s,
>> what expected
>>
>
> What is your expectation? Is it FC, iSCSI? How many paths? What is the IO
> scheduler in the VM? Is it using virtio-blk or virtio-SCSI?
> Y.
>
>
Peak bandwith no more than 140 MBytes/s, based on storage capabilities, but
I don't have to do a rude performance test. I need stability
Hosts has a mezzanine dual-port HBA (4 Gbit); each HBA connected to a
different FC-switch and the multipath connection has 2 active paths (one
for each HBA).

I confirm that with preallocated disk of the cloned VM I don't have indeed
the previous problems.
The same loop executed for about 66 times in a 10 minutes interval without
any problem registered on hosts
No message at all in /var/log/messages of both hosts.
My storage domain not compromised
It remains important the question about thin provisioning and SAN LUNs (aka
with LVM based disks).
In my opinion I shouldn't care of the kind of I/O made inside a VM and
anyway it shouldn't interfere with my storage domain, bringing down
completely my hosts/VMs.
In theory there could be an application inside a VM that generates
something similar to my loop and so would generate problems.
For sure I can then notify VM responsible about his/her workload, but it
should not compromise my virtual infrastructure
I could have an RDBMS inside a VM and a user that creates a big datafile
and that should imply many extend operations if the disk is thin
provisioned....

What about [irs] values? Where are they located, in vdsm.conf?
What are defaults for volume_utilization_percent and
volume_utilization_chunk_mb?
Did they change from 3.6 to 4.0 to 4.1?
What I should do after changing them to make them active?

Thanks in advance,
Gianluca
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