Re: [ceph-users] qemu-rbd and ceph striping

[Jason Dillaman]

On Thu, Oct 20, 2016 at 1:51 AM, Ahmed Mostafa
 wrote:
> different OSDs

PGs -- but more or less correct since the OSDs will process requests
for a particular PG sequentially and not in parallel.

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Jason
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Re: [ceph-users] qemu-rbd and ceph striping

[Ahmed Mostafa]

Does this also mean that strip count can be thought of as the number of
parrallel writes to different objects at different OSDs ?

Thank you

On Thursday, 20 October 2016, Jason Dillaman  wrote:

> librbd (used by QEMU to provide RBD-backed disks) uses librados and
> provides the necessary handling for striping across multiple backing
> objects. When you don't specify "fancy" striping options via
> "--stripe-count" and "--stripe-unit", it essentially defaults to
> stripe count of 1 and stripe unit of the object size (defaults to
> 4MB).
>
> The use-case for fancy striping settings for an RBD image are images
> that have lots of small, sequential IO. The rationale for that is that
> normally these small, sequential IOs will continue to hit the same PG
> until the object boundary is crossed. However, if you were to use a
> small stripe unit that matched your normal IO size (or a small
> multiple thereof), your small, sequential IO requests would be sent to
>  PGs -- spreading the load.
>
> On Wed, Oct 19, 2016 at 12:32 PM, Ahmed Mostafa
> > wrote:
> > Hello
> >
> > From the documentation i understand that clients that uses librados must
> > perform striping for themselves, but i do not understand how could this
> be
> > if we have striping options in ceph ? i mean i can create rbd images that
> > has configuration for striping, count and unite size.
> >
> > So my question is, if i created an RBD image that have striping enabled
> and
> > configured, will that make a difference with qemu-rbd ? by difference i
> mean
> > enhancing performance of my virtual machines i/o and allowing utilizing
> the
> > cluster resources
> >
> > Thank you
> >
> > ___
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> > ceph-users@lists.ceph.com 
> > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
> >
>
>
>
> --
> Jason
>
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Re: [ceph-users] qemu-rbd and ceph striping

[Jason Dillaman]

librbd (used by QEMU to provide RBD-backed disks) uses librados and
provides the necessary handling for striping across multiple backing
objects. When you don't specify "fancy" striping options via
"--stripe-count" and "--stripe-unit", it essentially defaults to
stripe count of 1 and stripe unit of the object size (defaults to
4MB).

The use-case for fancy striping settings for an RBD image are images
that have lots of small, sequential IO. The rationale for that is that
normally these small, sequential IOs will continue to hit the same PG
until the object boundary is crossed. However, if you were to use a
small stripe unit that matched your normal IO size (or a small
multiple thereof), your small, sequential IO requests would be sent to
 PGs -- spreading the load.

On Wed, Oct 19, 2016 at 12:32 PM, Ahmed Mostafa
 wrote:
> Hello
>
> From the documentation i understand that clients that uses librados must
> perform striping for themselves, but i do not understand how could this be
> if we have striping options in ceph ? i mean i can create rbd images that
> has configuration for striping, count and unite size.
>
> So my question is, if i created an RBD image that have striping enabled and
> configured, will that make a difference with qemu-rbd ? by difference i mean
> enhancing performance of my virtual machines i/o and allowing utilizing the
> cluster resources
>
> Thank you
>
> ___
> ceph-users mailing list
> ceph-users@lists.ceph.com
> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
>



-- 
Jason
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[ceph-users] qemu-rbd and ceph striping

[Ahmed Mostafa]

Hello

>From the documentation i understand that clients that uses librados must
perform striping for themselves, but i do not understand how could this be
if we have striping options in ceph ? i mean i can create rbd images that
has configuration for striping, count and unite size.

So my question is, if i created an RBD image that have striping enabled and
configured, will that make a difference with qemu-rbd ? by difference i
mean enhancing performance of my virtual machines i/o and allowing
utilizing the cluster resources

Thank you
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