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Hi,
Looks like there is some misinformation about exclusive lock feature, here is some information already on the mailing list:
The naming of the "exclusive-lock" feature probably implies too much compared to what it actually does. In reality, when you enable the "exclusive-lock" feature, only one RBD client is able to modify the image while the lock is held. However, that won't stop other RBD clients from *requesting* that maintenance operations be performed on the image (e.g. snapshot, resize).
Behind the scenes, librbd will detect that another client currently owns the lock and will proxy its request over to the current watch owner. This ensures that we only have one client modifying the image while at the same time not crippling other use cases. librbd also supports cooperative exclusive lock transfer, which is used in the case of qemu VM migrations where the image needs to be opened R/W by two clients at the same time.
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Jason Dillaman
Saludos Cordiales,
Xavier Trilla P. SiliconHosting ¿Un Servidor Cloud con SSDs, redundado y disponible en menos de 30 segundos? ¡Pruébalo ahora en Clouding.io!
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