[libvirt] [User question] Huge buffer size on KVM host
Avi Kivity
avi at redhat.com
Thu Aug 16 14:57:39 UTC 2012
On 08/16/2012 05:54 PM, Martin Wawro wrote:
>
> On Aug 15, 2012, at 2:57 PM, Avi Kivity wrote:
>
>>>
>>> We are using logical volumes and the cache is set to 'none'.
>>
>> Strange, that should work without any buffering.
>>
>> What the contents of
>>
>> /sys/block/sda/queue/hw_sector_size
>>
>> and
>>
>> /sys/block/sda/queue/logical_block_size
>>
>> ?
>>
>
> Hi Avi,
>
> It seems that the kernel on that particular machine is too old, those entries are
> not featured. We checked on a comparable setup with a newer kernel and both entries
> were set to 512.
>
> We also did have a third more thorough look on the caching. It turns out that the
> virt-manager does not seem to honor the caching adjusted in the GUI correctly.
> We disabled caching on all virtual devices for this particular VM and checking
> with "ps -fxal" revealed, that only one of those devices (and a rather small one too)
> had this set. We corrected this in the XML file directly and the buffer size
> currently resides at around 1.8 GB after rebooting the VM (the only virtio device
> not having the cache=none option set is now the (non-mounted) cdrom).
>
cc += libvirt-list
Is there a reason that cdroms don't get cache=none?
--
error compiling committee.c: too many arguments to function
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