Re: [ceph-users] OSDs with primary affinity 0 still used for primary PG

[Eric Goirand]

Hello Teun,

see below ..

On 02/15/2018 11:52 AM, Teun Docter wrote:

Hi David,

Thanks for explaining that, makes sense. (Though I guess the docs aren't very 
clear on that, but ok.) I have a follow up question on your suggestion to 
modify the crush map though.

I've seen a few examples on how to use crush rules to place primary copies on 
SSDs, and secondary copies on HDDs. In fact, one such example is in the main 
Ceph docs. However, they all seem to be based on the premise of having two 
types of OSD servers. One type would have *only* SSDs, and the other *only* 
HDDs.

However, that's not the scenario I'm investigating. I would like each of my OSD 
servers to be the same. Each would contain a number of SSDs, and a number of 
HDDs.

After reading up on crush rules, I think I understand how to setup a basic rule 
that would place the primary copy on a SSD, and the other copies on HDDs. But 
what I haven't figured out yet, is it possible to avoid placing one of the 
secondary copies on the same host that stores the primary copy?
The only way (as of now, before including the work of the bugzilla link 
[2]), to avoid having 2 copies on the same server (1 copy on a SSD drive 
and 1 copy on a HDD drive) would be to separate physically the servers 
that contain the SSD drives from the servers that contain the HDD drives.


You would then have to create your ruleset as you did previously but 
this time the two roots you start from (step take) are separated, thus 
no copy will end up on the same servers.


If you stick with the collocated drive setup, and if you still keep 
min_size equals to 2 in your pools, I would suggest to use replica 4 
instead of 3, to have access to all your data even if one server is down 
for maintenance.



I found an earlier thread [1] where you've hinted at using racks for this, but in that 
thread I think there is also some confusion about SSD/HDD only servers, versus 
"hybrid" servers. In addition, I found an issue in RedHats tracker [2], which 
also outlines this problem.

With my current understanding of crush rules, I'm not sure the setup I had in 
mind is feasible?

Thanks,
Teun

Thanks,
Eric.


[1] http://lists.ceph.com/pipermail/ceph-users-ceph.com/2017-April/017589.html
[2] https://bugzilla.redhat.com/show_bug.cgi?id=1517128

On 02/12/2018 09:17 PM, David Turner wrote:

If you look at the PGs that are primary on an OSD that has primary
affinity 0, you'll find that they are only on OSDs with primary affinity
of 0, so 1 of them has to take the reins or nobody would be responsible
for the PG.  To prevent this from happening, you would need to configure
your crush map in a way where all PGs are guaranteed to land on at least
1 OSD that doesn't have a primary affinity of 0.

On Mon, Feb 12, 2018 at 2:45 PM Teun Docter
> wrote:

 Hi,

 I'm looking into storing the primary copy on SSDs, and replicas on
 spinners.
 One way to achieve this should be the primary affinity setting, as
 outlined in this post:

 
https://www.sebastien-han.fr/blog/2015/08/06/ceph-get-the-best-of-your-ssd-with-primary-affinity

 So I've deployed a small test cluster and set the affinity to 0 for
 half the OSDs and to 1 for the rest:

 # ceph osd tree
 ID CLASS WEIGHT  TYPE NAME       STATUS REWEIGHT PRI-AFF
 -1       0.07751 root default
 -3       0.01938     host osd001
   1   hdd 0.00969         osd.1       up  1.0 1.0
   4   hdd 0.00969         osd.4       up  1.0       0
 -7       0.01938     host osd002
   2   hdd 0.00969         osd.2       up  1.0 1.0
   6   hdd 0.00969         osd.6       up  1.0       0
 -9       0.01938     host osd003
   3   hdd 0.00969         osd.3       up  1.0 1.0
   7   hdd 0.00969         osd.7       up  1.0       0
 -5       0.01938     host osd004
   0   hdd 0.00969         osd.0       up  1.0 1.0
   5   hdd 0.00969         osd.5       up  1.0       0

 Then I've created a pool. The summary at the end of "ceph pg dump"
 looks like this:

 sum 0 0 0 0 0 0 0 0
 OSD_STAT USED  AVAIL  TOTAL  HB_PEERS        PG_SUM PRIMARY_PG_SUM
 7        1071M  9067M 10138M [0,1,2,3,4,5,6]    192             26
 6        1072M  9066M 10138M [0,1,2,3,4,5,7]    198             18
 5        1071M  9067M 10138M [0,1,2,3,4,6,7]    192             21
 4        1076M  9062M 10138M [0,1,2,3,5,6,7]    202             15
 3        1072M  9066M 10138M [0,1,2,4,5,6,7]    202            121
 2        1072M  9066M 10138M [0,1,3,4,5,6,7]    195            114
 1        1076M  9062M 10138M [0,2,3,4,5,6,7]    161             95
 0        1071M  9067M 10138M [1,2,3,4,5,6,7]    194            102
 sum      8587M 72524M 8M

 Now, the OSDs for which the primary affinity is set to zero are
 acting as primary a lot less than the others.

Re: [ceph-users] OSDs with primary affinity 0 still used for primary PG

[Teun Docter]

Hi David,

Thanks for explaining that, makes sense. (Though I guess the docs aren't very 
clear on that, but ok.) I have a follow up question on your suggestion to 
modify the crush map though.

I've seen a few examples on how to use crush rules to place primary copies on 
SSDs, and secondary copies on HDDs. In fact, one such example is in the main 
Ceph docs. However, they all seem to be based on the premise of having two 
types of OSD servers. One type would have *only* SSDs, and the other *only* 
HDDs.

However, that's not the scenario I'm investigating. I would like each of my OSD 
servers to be the same. Each would contain a number of SSDs, and a number of 
HDDs.

After reading up on crush rules, I think I understand how to setup a basic rule 
that would place the primary copy on a SSD, and the other copies on HDDs. But 
what I haven't figured out yet, is it possible to avoid placing one of the 
secondary copies on the same host that stores the primary copy?

I found an earlier thread [1] where you've hinted at using racks for this, but 
in that thread I think there is also some confusion about SSD/HDD only servers, 
versus "hybrid" servers. In addition, I found an issue in RedHats tracker [2], 
which also outlines this problem.

With my current understanding of crush rules, I'm not sure the setup I had in 
mind is feasible?

Thanks,
Teun

[1] http://lists.ceph.com/pipermail/ceph-users-ceph.com/2017-April/017589.html
[2] https://bugzilla.redhat.com/show_bug.cgi?id=1517128

On 02/12/2018 09:17 PM, David Turner wrote:
> If you look at the PGs that are primary on an OSD that has primary 
> affinity 0, you'll find that they are only on OSDs with primary affinity 
> of 0, so 1 of them has to take the reins or nobody would be responsible 
> for the PG.  To prevent this from happening, you would need to configure 
> your crush map in a way where all PGs are guaranteed to land on at least 
> 1 OSD that doesn't have a primary affinity of 0.
> 
> On Mon, Feb 12, 2018 at 2:45 PM Teun Docter 
>  > wrote:
> 
> Hi,
> 
> I'm looking into storing the primary copy on SSDs, and replicas on
> spinners.
> One way to achieve this should be the primary affinity setting, as
> outlined in this post:
> 
> 
> https://www.sebastien-han.fr/blog/2015/08/06/ceph-get-the-best-of-your-ssd-with-primary-affinity
> 
> So I've deployed a small test cluster and set the affinity to 0 for
> half the OSDs and to 1 for the rest:
> 
> # ceph osd tree
> ID CLASS WEIGHT  TYPE NAME       STATUS REWEIGHT PRI-AFF
> -1       0.07751 root default
> -3       0.01938     host osd001
>   1   hdd 0.00969         osd.1       up  1.0 1.0
>   4   hdd 0.00969         osd.4       up  1.0       0
> -7       0.01938     host osd002
>   2   hdd 0.00969         osd.2       up  1.0 1.0
>   6   hdd 0.00969         osd.6       up  1.0       0
> -9       0.01938     host osd003
>   3   hdd 0.00969         osd.3       up  1.0 1.0
>   7   hdd 0.00969         osd.7       up  1.0       0
> -5       0.01938     host osd004
>   0   hdd 0.00969         osd.0       up  1.0 1.0
>   5   hdd 0.00969         osd.5       up  1.0       0
> 
> Then I've created a pool. The summary at the end of "ceph pg dump"
> looks like this:
> 
> sum 0 0 0 0 0 0 0 0
> OSD_STAT USED  AVAIL  TOTAL  HB_PEERS        PG_SUM PRIMARY_PG_SUM
> 7        1071M  9067M 10138M [0,1,2,3,4,5,6]    192             26
> 6        1072M  9066M 10138M [0,1,2,3,4,5,7]    198             18
> 5        1071M  9067M 10138M [0,1,2,3,4,6,7]    192             21
> 4        1076M  9062M 10138M [0,1,2,3,5,6,7]    202             15
> 3        1072M  9066M 10138M [0,1,2,4,5,6,7]    202            121
> 2        1072M  9066M 10138M [0,1,3,4,5,6,7]    195            114
> 1        1076M  9062M 10138M [0,2,3,4,5,6,7]    161             95
> 0        1071M  9067M 10138M [1,2,3,4,5,6,7]    194            102
> sum      8587M 72524M 8M
> 
> Now, the OSDs for which the primary affinity is set to zero are
> acting as primary a lot less than the others.
> 
> But what I'm wondering about is this:
> 
> For those OSDs that have primary affinity set to zero, why is the
> PRIMARY_PG_SUM column not zero?
> 
> # ceph -v
> ceph version 12.2.2 (cf0baba3b47f9427c6c97e2144b094b7e5ba)
> luminous (stable)
> 
> Note that I've created the pool after setting the primary affinity,
> and no data is stored yet.
> 
> Thanks,
> Teun
> 
> ___
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> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
> 
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Re: [ceph-users] OSDs with primary affinity 0 still used for primary PG

[David Turner]

If you look at the PGs that are primary on an OSD that has primary affinity
0, you'll find that they are only on OSDs with primary affinity of 0, so 1
of them has to take the reins or nobody would be responsible for the PG.
To prevent this from happening, you would need to configure your crush map
in a way where all PGs are guaranteed to land on at least 1 OSD that
doesn't have a primary affinity of 0.

On Mon, Feb 12, 2018 at 2:45 PM Teun Docter 
wrote:

> Hi,
>
> I'm looking into storing the primary copy on SSDs, and replicas on
> spinners.
> One way to achieve this should be the primary affinity setting, as
> outlined in this post:
>
>
> https://www.sebastien-han.fr/blog/2015/08/06/ceph-get-the-best-of-your-ssd-with-primary-affinity
>
> So I've deployed a small test cluster and set the affinity to 0 for half
> the OSDs and to 1 for the rest:
>
> # ceph osd tree
> ID CLASS WEIGHT  TYPE NAME   STATUS REWEIGHT PRI-AFF
> -1   0.07751 root default
> -3   0.01938 host osd001
>  1   hdd 0.00969 osd.1   up  1.0 1.0
>  4   hdd 0.00969 osd.4   up  1.0   0
> -7   0.01938 host osd002
>  2   hdd 0.00969 osd.2   up  1.0 1.0
>  6   hdd 0.00969 osd.6   up  1.0   0
> -9   0.01938 host osd003
>  3   hdd 0.00969 osd.3   up  1.0 1.0
>  7   hdd 0.00969 osd.7   up  1.0   0
> -5   0.01938 host osd004
>  0   hdd 0.00969 osd.0   up  1.0 1.0
>  5   hdd 0.00969 osd.5   up  1.0   0
>
> Then I've created a pool. The summary at the end of "ceph pg dump" looks
> like this:
>
> sum 0 0 0 0 0 0 0 0
> OSD_STAT USED  AVAIL  TOTAL  HB_PEERSPG_SUM PRIMARY_PG_SUM
> 71071M  9067M 10138M [0,1,2,3,4,5,6]192 26
> 61072M  9066M 10138M [0,1,2,3,4,5,7]198 18
> 51071M  9067M 10138M [0,1,2,3,4,6,7]192 21
> 41076M  9062M 10138M [0,1,2,3,5,6,7]202 15
> 31072M  9066M 10138M [0,1,2,4,5,6,7]202121
> 21072M  9066M 10138M [0,1,3,4,5,6,7]195114
> 11076M  9062M 10138M [0,2,3,4,5,6,7]161 95
> 01071M  9067M 10138M [1,2,3,4,5,6,7]194102
> sum  8587M 72524M 8M
>
> Now, the OSDs for which the primary affinity is set to zero are acting as
> primary a lot less than the others.
>
> But what I'm wondering about is this:
>
> For those OSDs that have primary affinity set to zero, why is the
> PRIMARY_PG_SUM column not zero?
>
> # ceph -v
> ceph version 12.2.2 (cf0baba3b47f9427c6c97e2144b094b7e5ba) luminous
> (stable)
>
> Note that I've created the pool after setting the primary affinity, and no
> data is stored yet.
>
> Thanks,
> Teun
>
> ___
> ceph-users mailing list
> ceph-users@lists.ceph.com
> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
>
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