Have you run sysstat on the command line of the filer?  (sysstat -x 1)  Are you getting a lot of "b" deferred back to back type CPs?  My understanding is that the filer starts rejecting new scsi requests when there are back-to-back deferred CPs (because there's no where to put them in memory locally).  That's when you get resets and errors on the hosts.

Flexshare will limit the IOs to that volume and will reduce the deferred CPs, which may prevent the resets and errors.  The host itself may not like that though-- there may be a timeout or some other tuning in iscsi that will help with this.

From: Alon Zeltser <alonz@emet.co.il>
To: Fred Grieco <fredgrieco@yahoo.com>; "toasters@teaparty.net" <toasters@teaparty.net>
Sent: Tuesday, December 6, 2011 9:43 AM
Subject: Re: limit i/o for lun or volume
Thank you for replay but as I wrote im aware of flexshare but I don't think it will help since this system is not impacting other systems and not compeating with other vms on resources
Its only hurting itself it doing so much iops and getting such bad latency that after few minutes its doing lun reset and the vm freezes and the user procces exit abnormally
I'm trying to limit the iops from this system so it wont load the Netapp so much and get better latency I don't care if it will take much longer to run

Thanks again

Fred Grieco <fredgrieco@yahoo.com> wrote:

Do you mean that there is a performance issue with that particular VM, or with other systems on the filer that are caused by I/O on that VM?

You should be able to use flex share to set a lower priority for a "cache-hogging" and reduce its impact on the other volumes.  On the command line, run "priority on."  Then run "priority set volume $volumename level=Low" for the problem volume.  This will give less priority to that volume in the write cache, free up the cache for other things, and (hopefully) reduce latency on those other volumes.


In your case, you'll need to have that RDM in its own volume.



________________________________
From: Alon Zeltser <alonz@emet.co.il>
To: toasters@teaparty.net
Sent: Tuesday, December 6, 2011 6:00 AM
Subject: limit i/o for lun or volume

Hi all
i have a situation of a virtual machine running on esx 4.0 over iscsi
this machine  (while the user is running his stuff)  is using a lot of
i/o on a very small netapp controller (2020) with only 5 data disks aggr
and getting very bad latency and eventually getting a lun reset errors
and the machine freeze for a few minutes
i have increased the timeouts from the windows side but it doesn't seems
to help
this application don't need so much i/o and can be run a 5.4k disk on an
old laptop but given the resources of netapp it uses them to the fullest
it is important to mention that this application is running over MSSQL
db and the i/o problem goes to rdm lun
my question: is there a way to limit the i/o of this machine from either
netapp side /vmware side / windows side / network side
i'm aweare of vmware storage i/o control but this is only supported in
vsphere 4.1 and an upgrade is not an options right now
i'm also aware of flexshare from the netapp side but i don't think
giving low priority to this volume will help in this case
is there other way you can think of to limit the i/o goes from vmware
virtual machine through iscsi to an rdm lun or his hosting volume?

thank you

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