blktap3 as a block device?

blktap3 as a block device?

[Darren Shepherd]

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So currently blktap2 can be used outside of Xen, but I don't think many
people do that.  I have a use case now where I must support KVM (I
currently run only Xen servers) and found the disk snapshotting to be not
as nice as what I can do with vhd's in blktap2 (and a half).  So I was
thinking of actually trying to just run blktap for the storage.  So I'm
pretty pleased with that solution and functionally it works just fine.

The problem now is blktap3.  So is there going to be any way to use blktap3
outside of Xen?  If blktap3 is the future I probably won't continue with my
blktap/kvm solution.

Thanks,
Darren

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Re: blktap3 as a block device?

[Fajar A. Nugraha]

On Sat, Nov 24, 2012 at 7:31 AM, Darren Shepherd
<darren.s.shepherd@gmail.com> wrote:
> So currently blktap2 can be used outside of Xen, but I don't think many
> people do that.  I have a use case now where I must support KVM (I currently
> run only Xen servers) and found the disk snapshotting to be not as nice as
> what I can do with vhd's in blktap2 (and a half).  So I was thinking of
> actually trying to just run blktap for the storage.  So I'm pretty pleased
> with that solution and functionally it works just fine.
>
> The problem now is blktap3.  So is there going to be any way to use blktap3
> outside of Xen?  If blktap3 is the future I probably won't continue with my
> blktap/kvm solution.

Since AFAIK blktap3 is not even in xen-unstable, personally I'd just
use something with more userbase and better tested. Something like
zfsonlinux. It has support for sparse zvols, as well as snapshot and
clones.

-- 
Fajar

Re: blktap3 as a block device?

[Darren Shepherd]

On Nov 23, 2012, at 4:39 PM, "Fajar A. Nugraha" <list@fajar.net> wrote:

> On Sat, Nov 24, 2012 at 7:31 AM, Darren Shepherd
> <darren.s.shepherd@gmail.com> wrote:
>> So currently blktap2 can be used outside of Xen, but I don't think many
>> people do that.  I have a use case now where I must support KVM (I currently
>> run only Xen servers) and found the disk snapshotting to be not as nice as
>> what I can do with vhd's in blktap2 (and a half).  So I was thinking of
>> actually trying to just run blktap for the storage.  So I'm pretty pleased
>> with that solution and functionally it works just fine.
>> 
>> The problem now is blktap3.  So is there going to be any way to use blktap3
>> outside of Xen?  If blktap3 is the future I probably won't continue with my
>> blktap/kvm solution.
> 
> Since AFAIK blktap3 is not even in xen-unstable, personally I'd just
> use something with more userbase and better tested. Something like
> zfsonlinux. It has support for sparse zvols, as well as snapshot and
> clones.
> 
> -- 
> Fajar

I'm using blktap2, but that's really besides the point.  

The more direct question is going forward with blktap3 is there going to be a way to see the blktap device as a block device in dom0?

Darren

Re: blktap3 as a block device?

[Ian Campbell]

On Sat, 2012-11-24 at 01:08 +0000, Darren Shepherd wrote:
> The more direct question is going forward with blktap3 is there going
> to be a way to see the blktap device as a block device in dom0?

There will have to be, e.g. to support pygrub and similar uses.

I'm not sure what form this will eventually take though (CCing Thanos,
blktap3 maintainer). Ideas which I've heard floating about are to have
tapdisk export an nbd server or supporting running a vbd device in dom0
in a loopback type mode.

Ian.

Re: blktap3 as a block device?

[Thanos Makatos]

> -----Original Message-----
> From: Ian Campbell
> Sent: 26 November 2012 10:45
> To: Darren Shepherd
> Cc: Fajar A. Nugraha; xen-devel@lists.xen.org; Thanos Makatos
> Subject: Re: [Xen-devel] blktap3 as a block device?
> 
> On Sat, 2012-11-24 at 01:08 +0000, Darren Shepherd wrote:
> > The more direct question is going forward with blktap3 is there going
> > to be a way to see the blktap device as a block device in dom0?
> 
> There will have to be, e.g. to support pygrub and similar uses.
> 
> I'm not sure what form this will eventually take though (CCing Thanos,
> blktap3 maintainer). Ideas which I've heard floating about are to have
> tapdisk export an nbd server or supporting running a vbd device in dom0
> in a loopback type mode.

Yes this is one of the possibilities; this functionality is already on blktap2.5 (where blktap3 is based on).

Another idea could be to use both blkfront and tapdisk on dom0, haven't considered that thoroughly though.

> 
> Ian.
> 

Re: blktap3 as a block device?

[Roger Pau Monné]

On 26/11/12 11:54, Thanos Makatos wrote:
> 
> 
>> -----Original Message-----
>> From: Ian Campbell
>> Sent: 26 November 2012 10:45
>> To: Darren Shepherd
>> Cc: Fajar A. Nugraha; xen-devel@lists.xen.org; Thanos Makatos
>> Subject: Re: [Xen-devel] blktap3 as a block device?
>>
>> On Sat, 2012-11-24 at 01:08 +0000, Darren Shepherd wrote:
>>> The more direct question is going forward with blktap3 is there going
>>> to be a way to see the blktap device as a block device in dom0?
>>
>> There will have to be, e.g. to support pygrub and similar uses.
>>
>> I'm not sure what form this will eventually take though (CCing Thanos,
>> blktap3 maintainer). Ideas which I've heard floating about are to have
>> tapdisk export an nbd server or supporting running a vbd device in dom0
>> in a loopback type mode.
> 
> Yes this is one of the possibilities; this functionality is already on blktap2.5 (where blktap3 is based on).
> 
> Another idea could be to use both blkfront and tapdisk on dom0, haven't considered that thoroughly though.

>From my point of view using blkfront on Dom0 should be used instead of
nbd. nbd is Linux specific, on the other hand all Dom0s have a blkfront
implementation.

Re: blktap3 as a block device?

[Stefano Stabellini]

On Sat, 24 Nov 2012, Darren Shepherd wrote:
> On Nov 23, 2012, at 4:39 PM, "Fajar A. Nugraha" <list@fajar.net> wrote:
> 
> > On Sat, Nov 24, 2012 at 7:31 AM, Darren Shepherd
> > <darren.s.shepherd@gmail.com> wrote:
> >> So currently blktap2 can be used outside of Xen, but I don't think many
> >> people do that.  I have a use case now where I must support KVM (I currently
> >> run only Xen servers) and found the disk snapshotting to be not as nice as
> >> what I can do with vhd's in blktap2 (and a half).  So I was thinking of
> >> actually trying to just run blktap for the storage.  So I'm pretty pleased
> >> with that solution and functionally it works just fine.
> >> 
> >> The problem now is blktap3.  So is there going to be any way to use blktap3
> >> outside of Xen?  If blktap3 is the future I probably won't continue with my
> >> blktap/kvm solution.
> > 
> > Since AFAIK blktap3 is not even in xen-unstable, personally I'd just
> > use something with more userbase and better tested. Something like
> > zfsonlinux. It has support for sparse zvols, as well as snapshot and
> > clones.
> > 
> > -- 
> > Fajar
> 
> I'm using blktap2, but that's really besides the point.  
> 
> The more direct question is going forward with blktap3 is there going to be a way to see the blktap device as a block device in dom0?

Yes, setting up a local frontend/backend connection in dom0: the backend is
blktap3, the frontend is the blkfront driver in the dom0 kernel