Hi Ceph, An erasure coded object stored in Firefly when it was first introduced must be decoded by all versions after Firefly. The encoding is done by erasure code plugins[1] and they evolve over time[2]. There needs to be a tool to check that all content encoded by a given version of the plugin can also be encoded by all subsequent versions of the same plugin.
The general idea is to archive objects created with a given Ceph version and check them will all subsequent versions, via a teuthology workunit run on all supported distributions and architectures. The ceph_erasure_code_non_regression command[3] creates an object and store it on disk or read an object from disk and checks that it can be read. It is used to create objects for all relevant variations of parameters of a given erasure code plugin. For instance: ceph_erasure_code_non_regression --stripe-width 4651 --parameter packetsize=32 --plugin jerasure --parameter technique=blaum_roth --parameter k=6 --parameter m=2 --create --base ../../ceph-erasure-code-corpus/v0.85-764-gf3a1532 ceph_erasure_code_non_regression --stripe-width 4651 --parameter packetsize=32 --plugin jerasure --parameter technique=liber8tion --parameter k=6 --parameter m=2 --create --base ../../ceph-erasure-code-corpus/v0.85-764-gf3a1532 etc. The script[4] and the objects are archived in a repository [5] that can be checked by later Ceph versions. The same script is used for checking and creating the objects so that there is no risk of confusion. These scripts are stored per version because a given script is developed for a given version of the plugins. The encode-decode-non-regression.sh[6] workunit uses these scripts when run from teuthology[7] and will run all of them, up to and including the currently running ceph version. This ultimately ensures that all archived objects can be read on all supported distributions and architectures. See also http://tracker.ceph.com/issues/9420 which is the ticket associated to this work. Although this all sound sensible to me right now, I would be very interested to hear about ideas to make this easier or better :-) Cheers [1] firefly erasure code plugins https://github.com/ceph/ceph/tree/firefly/src/erasure-code [2] giant erasure code plugins https://github.com/ceph/ceph/tree/v0.85/src/erasure-code [3] ceph_erasure_code_non_regression https://github.com/dachary/ceph/commit/497a82b2b3113dae724a43d8d4c7e430acf44120 [4] non-regression.sh https://github.com/dachary/ceph-erasure-code-corpus/blob/master/v0.80.5-226-g71d2562/non-regression.sh [5] ceph-erasure-code-corpus https://github.com/dachary/ceph-erasure-code-corpus [6] encode-decode-non-regression.sh https://github.com/dachary/ceph/commit/4f7a9f83fb1f037662861e8782c9b90566dcaa31 [7] non regression workload https://github.com/ceph/ceph-qa-suite/pull/136 -- Loïc Dachary, Artisan Logiciel Libre
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