On Thu, Feb 2, 2017 at 12:09 PM, Yaniv Kaul <ykaul@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@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@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