Re: [Luminous]How to choose the proper ec profile?

Michael <mehe.schmid@xxxxxx> · Mon, 30 Oct 2017 18:33:39 +0100



      On 10/30/2017 02:33 PM, shadow_lin
        wrote:
      
        Hi all,
        I am wondering how to choose the
          proper ec profile for new luminous ec rbd image.
        If I set the k too high what the
          draw back would be?
         
        Is it a good idea to set k=10 m=2?
          It sounds attempting the overhead of storage capacity is low
          and the redundancy is good.
      
      
      Hi,

      
      That is a consideration between how important your data is, how
      quickly you think you will notice [even if Ceph somehow doesn't or
      can't deal with it because of imperfect configuration or such] and
      how quickly you ultimately are done rebuilding redundancy.

      
      I'd suggest to imagine a bad scenario for how long it will take
      and just consider how nervous it'd make you to be down to x
      OSDs/hosts of redundancy for that duration.

      
      Apart from that, Ceph isn't a super stable super easy to
      comprehend type of software yet (no offense to anyone intended -
      you're overall doing a good job!). As far as I can guess, there
      could be the occasional moment when one extra copy allows you to
      use a simpler, more reliable "tabula rasa" approach to host / OSD
      problem fixing, while staying safe enough.

      
      shadow_lin wrote:

      
        What is the difference for storage
          safety(redundancy ) between k=10 m=2 and k=4 m=2?
      
      
      3 OSDs failing before you / Ceph restores them is a less likely
      event in a pool of 6 than one of 12. If you had k=10 million m=2
      with 12TB HDD, it'd probably take just some seconds to minutes
      until you have data loss.

      
      shadow_lin wrote:
      
         
        What would be a good ec profile
          for archive purpose(decent write perfomance and just ok read
          performace)?
      
      
      I don't actually know that - but the default is not bad if you ask
      me (not that it features writes faster than reads). Plus it lets
      you pick m.

      
      - Michael

      
_______________________________________________
ceph-users mailing list
ceph-users@xxxxxxxxxxxxxx
http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com