Some usability question

Some usability question

[Somnath Roy]

Hi,
Is there any way to know which OSD to map to which drive of a host from an Admin node ?
We know from command like say 'ceph osd tree' to identify till the host where an osd belongs to but not the disk. The workaround I have is to login to the corresponding node and see the mount points to identify. Is this the best one or am I missing any command ?
If we can depict a tree view (similar to 'ceph osd tree') from pool to disk level (pool -> hosts ( and the crush buckets hierarchy) -> osds -> disks), user can easily find out their crush map is working as expected on a specific pool (say cache tier).

Second question,  regarding Erasure coded pool a certain amount of storage could be lost because of padding. I think it will be helpful if we can show how much is lost because of the variant client workload with the help of a command. This information can help user to choose the erasure coded profile (as it is dependent on K value) accordingly. Presently, rados object can't identify what is valid (and what not), so it could be a lot of effort, but is it worth ?  Any thoughts ?

Thanks & Regards
Somnath



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Re: Some usability question

[Sage Weil]

On Thu, 26 Feb 2015, Somnath Roy wrote:
> Hi,

> Is there any way to know which OSD to map to which drive of a host from 
> an Admin node ? We know from command like say 'ceph osd tree' to 
> identify till the host where an osd belongs to but not the disk. The 
> workaround I have is to login to the corresponding node and see the 
> mount points to identify. Is this the best one or am I missing any 
> command ? If we can depict a tree view (similar to 'ceph osd tree') from 
> pool to disk level (pool -> hosts ( and the crush buckets hierarchy) -> 
> osds -> disks), user can easily find out their crush map is working as 
> expected on a specific pool (say cache tier).

The closest is 'ceph osd metadata <id>' which gives you a bunch of random 
info about the OSD.  Right now it just gives you the path, which is always 
/var/lib/ceph/osd/ceph-NNN, but that could be expanded to try to map that 
back to a device, probably.  Search for 'metadata' in osd/OSD.cc.

> Second question, regarding Erasure coded pool a certain amount of 
> storage could be lost because of padding. I think it will be helpful if 
> we can show how much is lost because of the variant client workload with 
> the help of a command. This information can help user to choose the 
> erasure coded profile (as it is dependent on K value) accordingly. 
> Presently, rados object can't identify what is valid (and what not), so 
> it could be a lot of effort, but is it worth ?  Any thoughts ?

Hmm.  Not super trivial.  You could take the size of each object and 
calculate how much got padded to fill out the stripe, or probably do 
something that calculates what the average amount wasted would be for a 
uniform distribution of sizes.  Meh...  how important is this?

sage

RE: Some usability question

[Somnath Roy]

Thanks !
<<inline

-----Original Message-----
From: Sage Weil [mailto:sage@newdream.net]
Sent: Thursday, February 26, 2015 1:20 PM
To: Somnath Roy
Cc: Ceph Development
Subject: Re: Some usability question

On Thu, 26 Feb 2015, Somnath Roy wrote:
> Hi,

> Is there any way to know which OSD to map to which drive of a host
> from an Admin node ? We know from command like say 'ceph osd tree' to
> identify till the host where an osd belongs to but not the disk. The
> workaround I have is to login to the corresponding node and see the
> mount points to identify. Is this the best one or am I missing any
> command ? If we can depict a tree view (similar to 'ceph osd tree')
> from pool to disk level (pool -> hosts ( and the crush buckets
> hierarchy) -> osds -> disks), user can easily find out their crush map
> is working as expected on a specific pool (say cache tier).

The closest is 'ceph osd metadata <id>' which gives you a bunch of random info about the OSD.  Right now it just gives you the path, which is always /var/lib/ceph/osd/ceph-NNN, but that could be expanded to try to map that back to a device, probably.  Search for 'metadata' in osd/OSD.cc.
[Somnath] Sure, I will see if I can add this.

> Second question, regarding Erasure coded pool a certain amount of
> storage could be lost because of padding. I think it will be helpful
> if we can show how much is lost because of the variant client workload
> with the help of a command. This information can help user to choose
> the erasure coded profile (as it is dependent on K value) accordingly.
> Presently, rados object can't identify what is valid (and what not),
> so it could be a lot of effort, but is it worth ?  Any thoughts ?

Hmm.  Not super trivial.  You could take the size of each object and calculate how much got padded to fill out the stripe, or probably do something that calculates what the average amount wasted would be for a uniform distribution of sizes.  Meh...  how important is this?

[Somnath] This is one of the concern came up during our qualification with erasure coding pool. We need to quantify the actual storage gain for different workload in case of erasure coding vs replicated. I was thinking if it is trivial to do , but, if not,  not a high priority.

sage

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Re: Some usability question

[Nigel Williams]

On 27/02/2015 8:05 AM, Somnath Roy wrote:
> Is there any way to know which OSD to map to which drive of a host from an Admin node ?

still requires a ssh login, but I guess you know about ceph-disk list?

RE: Some usability question

[Somnath Roy]

Hi Nigel,
Yes, but I didn't actually noticed that it is giving osd numbers as well. I probably always used it before installation to list the disks :-)
Thanks, this is helpful.

Regards
Somnath

-----Original Message-----
From: ceph-devel-owner@vger.kernel.org [mailto:ceph-devel-owner@vger.kernel.org] On Behalf Of Nigel Williams
Sent: Thursday, February 26, 2015 3:55 PM
To: ceph-devel@vger.kernel.org
Subject: Re: Some usability question

On 27/02/2015 8:05 AM, Somnath Roy wrote:
> Is there any way to know which OSD to map to which drive of a host from an Admin node ?

still requires a ssh login, but I guess you know about ceph-disk list?


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RE: Some usability question

[Somnath Roy]

Hi,
One more issue I faced in case of Cache tiering.
I couldn't find any list/show command that will show the existing cache tiers in the cluster along with its backup pool.
Am I missing anything ?

-----Original Message-----
From: Somnath Roy
Sent: Thursday, February 26, 2015 4:07 PM
To: 'Nigel Williams'; ceph-devel@vger.kernel.org
Subject: RE: Some usability question

Hi Nigel,
Yes, but I didn't actually noticed that it is giving osd numbers as well. I probably always used it before installation to list the disks :-) Thanks, this is helpful.

Regards
Somnath

-----Original Message-----
From: ceph-devel-owner@vger.kernel.org [mailto:ceph-devel-owner@vger.kernel.org] On Behalf Of Nigel Williams
Sent: Thursday, February 26, 2015 3:55 PM
To: ceph-devel@vger.kernel.org
Subject: Re: Some usability question

On 27/02/2015 8:05 AM, Somnath Roy wrote:
> Is there any way to know which OSD to map to which drive of a host from an Admin node ?

still requires a ssh login, but I guess you know about ceph-disk list?


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