using secondary OSDs for reading
Hi, Quoting the page https://docs.ceph.com/en/latest/architecture/
location query over a chatty session. The CRUSH algorithm allows a client to compute where objects should be stored, and enables the client to contact the primary OSD to store or retrieve the objects.
So clients contact the *primary* OSD to store/retrieve objects. Why do clients not contact secondary (or even tertiary) OSDs for reading data? Would that not (potentially) result in greatly improved performance..? I'm sure there are good reasons for the current behaviour, but it seems logical, since you have multiple copies of the same data, to try and use the nearest copy? Curious :-) MJ
I have the same question about when recovery is going to happen! I think recovering from second and third OSD can lead to not impact client IO too when the primary OSD has another recovery ops! On Tue, Feb 9, 2021 at 1:28 PM mj <lists@merit.unu.edu> wrote:
Hi,
Quoting the page https://docs.ceph.com/en/latest/architecture/
location query over a chatty session. The CRUSH algorithm allows a client to compute where objects should be stored, and enables the client to contact the primary OSD to store or retrieve the objects.
So clients contact the *primary* OSD to store/retrieve objects.
Why do clients not contact secondary (or even tertiary) OSDs for reading data? Would that not (potentially) result in greatly improved performance..?
I'm sure there are good reasons for the current behaviour, but it seems logical, since you have multiple copies of the same data, to try and use the nearest copy?
Curious :-)
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Den ons 10 feb. 2021 kl 18:05 skrev Seena Fallah <seenafallah@gmail.com>:
I have the same question about when recovery is going to happen! I think recovering from second and third OSD can lead to not impact client IO too when the primary OSD has another recovery ops!
Those OSDs (the 2nd and 3rd) are obviously someone else primary. -- May the most significant bit of your life be positive.
But I think they can have no recovery ops. On Wed, Feb 10, 2021 at 9:28 PM Janne Johansson <icepic.dz@gmail.com> wrote:
Den ons 10 feb. 2021 kl 18:05 skrev Seena Fallah <seenafallah@gmail.com>:
I have the same question about when recovery is going to happen! I think recovering from second and third OSD can lead to not impact client IO too when the primary OSD has another recovery ops!
Those OSDs (the 2nd and 3rd) are obviously someone else primary.
-- May the most significant bit of your life be positive.
Yes but this can speed up and balance the recovery ops to all OSDs and because it's a read op for the secondary or third OSD this can't be much heartful! On Wed, Feb 10, 2021 at 10:03 PM Janne Johansson <icepic.dz@gmail.com> wrote:
Den ons 10 feb. 2021 kl 19:09 skrev Seena Fallah <seenafallah@gmail.com>:
But I think they can have no recovery ops.
No, but they would still have client ops even if there was no backfills or recovery anywhere on the OSD.
-- May the most significant bit of your life be positive.
participants (3)
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Janne Johansson
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mj
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Seena Fallah