Thanks Loic.
On Mon, Sep 1, 2014 at 11:31 PM, Loic Dachary <loic at dachary.org> wrote:
> Hi John,
>
> On 02/09/2014 05:29, Jakes John wrote:> Hi,
> > I have some general questions regarding the crush map. It would be
> helpful if someone can help me out by clarifying them.
> >
> > 1. I saw that a bucket 'host' is always created for the crush maps
> which are automatically generated by ceph. If I am manually creating
> crushmap, do I need to always add a bucket called ' host' ? As I was
> looking through the source code, I didn't see any need for this. If not
> necessary, can osd's of the same host be split into mulitple buckets?
> >
> > eg : Say host 1 has four osd's- osd.0,osd.1,osd.2, osd.3
> > host 2 has four osd's-
> osd.4,osd.5,osd.6,osd.7
> >
> > and create two buckets -
> >
>
> HostGroup bucket1- {osd.0, osd.1,osd.4,osd.5}
> > HostGroup bucket2-{osd.2,osd.3,osd.6,osd.7} where HostGroup is new
> bucket type instead of the default 'host' type.
> >
> >
> > Is this configuration possible or invalid? If this is possible, I can
> group SSD's of all hosts into 1 bucket and HDD's into other.
>
> What you describe seem possible but I'm not sure what problem you are
> trying to solve. The crush map described at
>
>
> http://ceph.com/docs/master/rados/operations/crush-map/#placing-different-pools-on-different-osds
>
> is not what you want ?
>
No. I have seen this before. In the example, each of the hosts had either
only SSD's or only HDD's. In my example, host1 has two ssd's and two hdd's.
Similar is the case for host2. So, If I need to have a bucket for SSD's
only, I need to create a bucket as stated above.
HostGroup bucket1- {osd.0, osd.1,osd.4,osd.5}
Is this possible?
>
> > 2. I have read in Ceph docs that same osd is not advised to be part of
> two buckets(two pools).
>
> A single OSD should be in a single bucket in the crush map indeed. But it
> is common for two OSD to be part of multiple pools. The pools are
> associated with a ruleset and each ruleset can choose in the same set of
> OSDs.
>
> > Is there any reason for it? But,I couldn't find this limitation in the
> source code.
>
> There is no limitation in the code but the crush function has been tested
> and used with a hierarchy where leaf nodes are not part of more than one
> bucket.
>
>
> Cheers
>
> > eg:osd.0 is in bucket1 and bucket2.
> >
> > Is this configuration possible or invalid? If this is possible, I have
> the flexibility to have group data which are written to different pools.
>
So, it is possible right?. I have plans to have third replica to stay in a
particular rack for all pools.( common to all pools)
> >
> > 3. Is it possible to exclude or include a particular osd/host/rack in
> the crush mapping?.
> >
> > eg: I need to have third replica always in rack3 (a specified
> row/rack/host based on requirements) . First two can be chosen randomly
> >
> > If possible, how can I configure it?
> >
>
Any ideas for 3,4,5 ?
> >
> > 4. It is said that osd weights must be configured based on the storage.
> Say if I have SSD of 512 GB and HDD of 1 TB and if I configure .5 and 1
> respectively, am I treating both SSD and HDD equally? How do I prioritize
> SSD over HDD?
> >
>
> > 5. Continuing from 4), If i have mix of SSD's and HDD's in the same
> host, what are the best ways possible to utilize the SSD capabilities in
> the ceph cluster?
> >
> >
>
> > Looking forward to your help,
> >
> > Thanks,
> >
> >
> >
> >
> >
> >
> >
> >
> >
> > _______________________________________________
> > ceph-users mailing list
> > ceph-users at lists.ceph.com
> > http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
> >
>
> --
> Lo?c Dachary, Artisan Logiciel Libre
>
>
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