Hi Loic, Thanks for your response. The idea for this cluster will be for our VM Replica storage in our secondary site. Initially we are planning to have a 40 disk EC pool sitting behind a cache pool of around 1TB post replica size. This storage will be presented as RBD's and then exported as a HA iSCSI target to ESX hosts. The VM's will be replicated from our primary site via a software product called Veeam. I'm hoping that the 1TB cache layer should be big enough to hold most of the hot data meaning that the EC pool shouldn't see a large amount of IO, just the trickle of the cache layer flushing back to disk. We can switch back to a 3 way replica pool if the EC pool doesn't work out for us, but we are interested in testing out the EC technology. I hope that provides an insight to what I am trying to achieve. Thanks, Nick -----Original Message----- From: ceph-users [mailto:ceph-users-bounces@xxxxxxxxxxxxxx] On Behalf Of Loic Dachary Sent: 05 December 2014 16:23 To: Nick Fisk; 'Ceph Users' Subject: Re: Erasure Encoding Chunks On 05/12/2014 16:21, Nick Fisk wrote:> Hi All, > > > > Does anybody have any input on what the best ratio + total numbers of Data + Coding chunks you would choose? > > > > For example I could create a pool with 7 data chunks and 3 coding chunks and get an efficiency of 70%, or I could create a pool with 17 data chunks and 3 coding chunks and get an efficiency of 85% with a similar probability of protecting against OSD failure. > > > > What?s the reason I would choose 10 total chunks over 20 chunks, is it purely down to the overhead of having potentially double the number of chunks per object? Hi Nick, Assuming you have a large number of OSD (a thousand or more) with cold data, 20 is probably better. When you try to read the data it involves 20 OSDs instead of 10 but you probably don't care if reads are rare. Disclaimer : I'm a developer not an architect ;-) It would help to know the target use case, the size of the data set and the expected read/write rate. Cheers -- Loïc Dachary, Artisan Logiciel Libre _______________________________________________ ceph-users mailing list ceph-users@xxxxxxxxxxxxxx http://lists.ceph.com/listinfo.cgi/ceph-users-ceph.com
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