[vbox-dev] is virtstor being implemented?

[Klaus Espenlaub]

On 19.10.2010 09:15, Huihong Luo wrote:
> Achim,
> Thanks for the clarification.
> I was playing Microsoft Virtual Server 2005 SP1 this morning, and they
> have SCSI Shunt Driver, a kind of virtstor, and it causes quite a
> difference when using it, so I was wondering there might be something.
> Now I know it must be due to their poor implementation on regular disk
> emulation.
> VBox team is superb ! The disk performance is impressive !
> There is one minor thing about fixed size disk creation, it seems to be
> quite slow. 10G VHD fixed size takes about 30 mins. Is this normal?
> Microsoft's VHD driver on windows 7 seems to be much faster. I know this
> isn't very important, as it's not used at runtime.

What? "VHD fixed" creation in VirtualBox is super fast, for 10G it takes 
under a second here (VBoxManage createhd /path/to/test.vhd --size 10240 
--format vhd --variant fixed). In fact we have a TODO in the code to 
make it slower. At the moment the code just sets the file size to the 
required capacity, making it a sparse file. We made VERY bad experience 
with sparse file performance on Windows, writing a single 512 byte block 
to such a file on NTFS can take several minutes, which might be your 
real problem...

We don't really consider VHD a very important image format. The code is 
well tested and has generally good performance, however it hasn't seen 
much optimization. I personally wouldn't use it unless I absolutely have 
to, and the only reason would be existing images.

Klaus

>
>
> --- On *Mon, 10/18/10, Achim Hasenmüller
> /<achim.hasenmueller at oracle.com>/* wrote:
>
>
>     From: Achim Hasenmüller <achim.hasenmueller at oracle.com>
>     Subject: Re: [vbox-dev] is virtstor being implemented?
>     To: "Huihong Luo" <huisinro at yahoo.com>
>     Cc: "Alexey Eromenko" <al4321 at gmail.com>, "Liang Suilong"
>     <liangsuilong at gmail.com>, vbox-dev at virtualbox.org
>     Date: Monday, October 18, 2010, 11:57 PM
>
>     What you describe is basically how SATA and SCSI/SAS work :-)
>
>     Honestly, we don't see any reason to implement virtstor. We do not
>     expect any performance advantages and whereas a network driver is
>     easy to add/change after install, a disk controller is more
>     complicated and less user friendly.
>
>     I would say that there isn't much out there that can compete with
>     VBox when it comes to disk performance. Our performance work is now
>     mostly focused around network as this is clearly where we have room
>     for improvement. We want to continue to improve the E1000 device but
>     for ultimate performance, our efforts are currently focused on
>     virtio. Once we can make full use of receive and send offloading, we
>     should be good.
>
>     Achim
>
>     On Oct 19, 2010, at 8:14 , Huihong Luo wrote:
>
>>     yes, it's the speed reason. In theory, virtstor is supposed to be
>>     fast. However, since vbox is already doing so well on disk, I am
>>     not sure how much further can be improved.
>>     In theory, virtstor bypasses many calls, and goes directly to the
>>     cheese, i.e., block i/o data transfer. The performance depends how
>>     well the mechanism for the transfer between vm and host, which is
>>     why I mentioned share folders. (btw, I know the difference between
>>     file sysem and block driver, I do that for a living). What I mean
>>     is that we can use the same large data transfer mechanism if
>>     shared folder's performance is very good.
>>     for example, a user app wants to write 10k data to the disk, it
>>     goes to the virtio driver after a few calls in windows, if the
>>     virtstor driver can efficiently (directly) transfer the buffer to
>>     the host, perhaps through memory sharing, or pinned physical
>>     pages, this should improve the performance.
>>     About the guest drivers, windows 7 and vista sp1 introduced some
>>     new models that should be even faster than kvm's implementation.
>>
>>
>
>
>
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