[Lustre-devel] Control file striping

[White, Cliff <cliff.white@intel.com>]

Creating/destroying pools must be done as per the manual, from MDS.
Do you need to frequently create/destroy pools, or would you have a fixed setup?

The normal method is to map various pools (and other striping policies) to directories, then user space applications
can access specific pools by pointing at the requisite directory, thus requiring no special API.
Once pools are created, the directory creation/striping is all done on a client via lfs setstripe, the liblustreapi can
also be used by clients to set striping via C calls.

Best
cliffw


On Nov 5, 2012, at 10:01 AM, Kalyana C <ckkccf at gmail.com<mailto:ckkccf@gmail.com>>
 wrote:

> Have you considered using a combination of OST Pools and striping fit your needs?

This is the only way possible that I currently know of.

But is it possible to manage OST pools via an API call? Can it be done from a client under a normal user application? Or does it have the same restrictions as described at http://wiki.lustre.org/index.php/Creating_and_Managing_OST_Pools

Regards,
Kalyan

On Mon, Nov 5, 2012 at 11:57 AM, Ben Evans <Ben.Evans at terascala.com<mailto:Ben.Evans@terascala.com>> wrote:
Have you considered using a combination of OST Pools and striping fit
your needs?

-----Original Message-----
From: lustre-devel-bounces@lists.lustre.org<mailto:lustre-devel-bounces@lists.lustre.org>
[mailto:lustre-devel-bounces at lists.lustre.org<mailto:lustre-devel-bounces@lists.lustre.org>] On Behalf Of Atchley,
Scott
Sent: Monday, November 05, 2012 12:47 PM
To: Kalyana C
Cc: lustre-devel at lists.lustre.org<mailto:lustre-devel@lists.lustre.org>
Subject: Re: [Lustre-devel] Control file striping

On Nov 3, 2012, at 1:41 PM, Kalyana C <ckkccf at gmail.com<mailto:ckkccf@gmail.com>> wrote:

> Hello,
>
> I am trying to figure out a way to:
>
> set striping across a set of OSTs of my choice.
>
> lfs setstripe command and API call does not allow for this currently.
The user can only set the starting OST through the index parameter. I
appreciate why there is no such feature currently; you do not want to
let the users have control on how OSTs are used since it can result in
OST usage imbalance.
>
> However, I do have a valid usage case for such a feature and I am
trying to figure out the best way to do it.

I have a valid use for it as well. It would be nice to have this feature
back.

Scott

>
> One way to achieve the same result is through the use of OST pools.
However, the userland tools do not work from a client node, it has to be
run on the MGS. There are also other restrictions as described here:
http://wiki.lustre.org/index.php/Creating_and_Managing_OST_Pools
>
> I am also digging through the Lustre source and header files to see if
there are other (undocumented) ways to do this.
>
> So, my questions are as follows:
>
> 1) Is there currently a way for a user to control the striping of a
file / directory on a selected set of OSTs? If yes, is it possible to do
it through an API call or a command line utility?
>
> 2) If answer to (1) is No, Is there a way to do this with admin rights
from the MDS or client nodes?
>
> 3) If pools are the only way to achieve this, is there an API call to
create, manage and destroy pools from a user application? Is there any
impact on performance of MDS components if pools are dynamically created
and deleted on demand? Can the API be called from a client node (root or
user) or does it have to be on the MGS?
>
> Thank you.
>
> Regards,
> Kalyana Chadalavada
>
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