Monthly Archives: March 2017

Predicting Ceph PG placement

When creating a new Ceph pool, deciding for the number of PG requires some thinking to ensure there are a few hundred PGs per OSD. The distribution can be verified with crush analyze as follows: $ crush analyze –rule data … Continue reading

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How many objects will move when changing a crushmap ?

After a crushmap is changed (e.g. addition/removal of devices, modification of weights or tunables), objects may move from one device to another. The crush compare command can be used to show what would happen for a given rule and replication … Continue reading

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Predicting which Ceph OSD will fill up first

When a device is added to Ceph, it is assigned a weight that reflects its capacity. For instance if osd.1 is a 1TB disk, its weight will be 1.0 and if osd.2 is a 4TB disk, its weight will be … Continue reading

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