[Users] Virtual Disk creation - really slow (config issue?) e.g 20GB disk created in 23 mins - NFS server/Gigabit switch - can anyone suggest why speed is so slow ? (at this rate it would take 1hr 40 mins to create a 100GB disk...)

[Gary Scarborough]

It can.  I have seldom had need to worry about it.  Most data centers have
battery backups to keep power outages from crashing systems. I am also not
sure if its any more or less of a risk than iscsi, except you may not be
able to tell right away.  async works by basically lying to the client
about the read/write.  Keep in mind that the read/write may be into a
virtual machine in this case.  Even if all packets are accounted for, not
completing the full stream of writing could lead to a corrupt VM filesystem
anyway.  In my mind, its worth the risk for the speed.  This is also why we
do backups.


On Fri, Mar 23, 2012 at 7:48 AM, Morgan Cox <morgancoxuk at gmail.com> wrote:

> Thank you Gary.
>
> After re-mounting the NFS share with async it dramatically increased the
> speed !
>
> I can now create a 10GB virtual disk in 2 mins (rather than 10 mins)
>
> Is using the async option more likely to cause data corruption though ?
>
> Many thanks
>
> Regards
>
> On 22 March 2012 21:54, Gary Scarborough <virtuallymad at gmail.com> wrote:
>
>>
>>
>> On Thu, Mar 22, 2012 at 12:59 PM, Morgan Cox <morgancoxuk at gmail.com>wrote:
>>
>>> Hi.
>>>
>>> After my many issues with spice I have finally sorted them out.
>>>
>>> Now I am having an issue with the speed of virtual disk creation - when
>>> I go to create a virtual disk it takes a long time (far to long to
>>> be usable)
>>>
>>> My setup is as following
>>>
>>> 3 servers:-
>>>
>>> 1 Frontend (ovirt engine) - Fedora 16    - external + local IP
>>> (91.215.xxx.xx + 10.0.0.10)
>>> 1 Ovirt node (using the node .iso)   - external + local IP (ovirtmgmt
>>> (eth0) - 91.215.xxx.xxx  and LAN (eth1) - 10.0.0.101)
>>> 1 NFS storage - external + local IP - I attached the storage using the
>>> Local IP (10.0.0.190)
>>>
>>> All servers are connected via a Gigabit switch (so speed should be
>>> better)
>>>
>>> I can scp between servers far faster - I'm almost sure its due to the
>>> node ovirtmgmt address being an external (internet ip) and not LAN ip.
>>> - therefore the traffic is not just going over the gigabit switch but via
>>> the core router in the DC...
>>>
>>> Can anyone suggest how I can 'debug' where the slowness is coming from
>>>
>>> On my NFS server I have it setup like (in /etc/exports)
>>>
>>> /storage1       *(rw,sync,no_subtree_check)
>>>
>>> I had previous tried setting up the node on a LAN IP previously and it
>>> caused spice to not work - as the node had no internet access / DNS - I
>>> also tried making the frontend server a gateway (and using -  iptables -t
>>> nat -A POSTROUTING -j MASQUERADE ) - this also cause spice to not work (as
>>> it always tried to connect to the 10.0.0.x address from my desktop - and
>>> fail..)
>>>
>>> Any hints/help will be welcomed
>>>
>>> Cheers
>>>
>>>
>>>
>>> _______________________________________________
>>> Users mailing list
>>> Users at ovirt.org
>>> http://lists.ovirt.org/mailman/listinfo/users
>>>
>>>
>> You could try async instead of sync.  You could also try thin
>> provisioning.
>>
>> --
>> Gary Scarborough
>> IST Lab Manager
>> Rochester Institute of Technology
>> Rochester NY
>>
>
>


-- 
Gary Scarborough
IST Lab Manager
Rochester Institute of Technology
Rochester NY
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