Re: questions on editing crushmap for ceph cache tier

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You are close...

I've done it by creating a new SSD root in the CRUSH map, then put the
SSD OSDs into a -ssd entry. I then created a new crush rule to choose
from the SSD root, then have the tiering pool use that rule. If you
look at the example in the document and think of ceph-osd-ssd-server-1
and ceph-osd-platter-server-1 as the same physical server with just
logical separation, you can follow the rest of the example. You will
need to modify either the ceph.conf to have the ssd OSDs have a
different CRUSH map location or write a location script to do it
automatically [1].

ceph.conf example:
[osd.70]
        crush location = root=ssd host=nodez-ssd

To do it programmaticly, you can use /usr/bin/ceph-crush-location as a
base. I extended it by finding the device, then searching through
hdparam to see if the rotation was greater than zero. If it wasn't
then I output the hostname with the ssd portion, otherwise just the
hostname. It was only a few lines of code, but I can't find it right
now. I was waiting for ACLs to be modified so that I could query the
data center location from our inventory management system (that was a
few months ago) and I'm still waiting.

[1] http://lists.ceph.com/pipermail/ceph-users-ceph.com/2015-January/045673.html
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Robert LeBlanc
PGP Fingerprint 79A2 9CA4 6CC4 45DD A904  C70E E654 3BB2 FA62 B9F1


On Wed, Jul 29, 2015 at 9:21 PM, van <chaofanyu@xxxxxxxxxxx> wrote:
> Hi, list,
>
>  Ceph cache tier seems very promising for performance.
>  According to
> http://ceph.com/docs/master/rados/operations/crush-map/#placing-different-pools-on-different-osds
> , I need to create a new pool based on SSD OSDs。
>
>  Currently, I’ve two servers with several HDD-based OSDs. I mean to add one
> SSD-based OSD for each server, and then use these two OSDs to build a cache
> pool.
>  But I’ve found problems editing crushmap.
>  The example in the link use two new hosts to build SSD OSDs and then create
> a new ruleset take the new hosts.
>  But in my environment, I do not have new servers to use.
>  Can I create a ruleset choose part of OSDs in a host?
>  For example, as the crushmap shown below, osd.2 and osd.5 are new added
> SSD-based OSDs, how can I create a ruleset choose these two OSDs only and
> how can I avoid default ruleset to choose osd.2 and osd.5?
>  Is this possible, or I have to add a new server to deploy cache tier?
>  Thanks.
>
> host node0 {
>   id -2
>   alg straw
>   hash 0
>   item osd.0 weight 1.0 # HDD
>   item osd.1 weight 1.0 # HDD
>   item osd.2 weight 0.5 # SSD
> }
>
> host node1 {
>   id -3
>   alg straw
>   hash 0
>   item osd.3 weight 1.0 # HDD
>   item osd.4 weight 1.0 # HDD
>   item osd.5 weight 0.5 # SSD
> }
>
> root default {
>         id -1           # do not change unnecessarily
>         # weight 1.560
>         alg straw
>         hash 0  # rjenkins1
>         item node0 weight 2.5
>         item node1 weight 2.5
> }
>
>  # typical ruleset
>  rule replicated_ruleset {
>         ruleset 0
>         type replicated
>         min_size 1
>         max_size 10
>         step take default
>         step chooseleaf firstn 0 type host
>         step emit
> }
>
>
>
> van
> chaofanyu@xxxxxxxxxxx
>
>
>
>
> _______________________________________________
> ceph-users mailing list
> ceph-users@xxxxxxxxxxxxxx
> http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
>
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