Hi, I'm doing a master's degree in distributed file systems, specifically CephFS in HPC, and I have some questions about the metadata migration process of MDSes that balances the MDS cluster.
* Sage Weil Ph.D. thesis' and the documentation in the Ceph website say that before migrating to balance the MDS, the first step is to freeze the subtree and when the migration is complete, to unfreeze it. Doesn't it affect the performance since the subtree stays unavaliable until migration is over?
* Could you explain why the freezes are required at all?
* Is It possible to change the migration process to migrate a copy of the inodes and then migrate inodes that have modifications after the migration? Like taking a snapshot of the subtree and migrate that, and then migrate any changes that happened after the snapshot migration is done, reducing the time spent with the subtree frozen.
* Sage Weil Ph.D. thesis' and the documentation in the Ceph website say that before migrating to balance the MDS, the first step is to freeze the subtree and when the migration is complete, to unfreeze it. Doesn't it affect the performance since the subtree stays unavaliable until migration is over?
* Could you explain why the freezes are required at all?
* Is It possible to change the migration process to migrate a copy of the inodes and then migrate inodes that have modifications after the migration? Like taking a snapshot of the subtree and migrate that, and then migrate any changes that happened after the snapshot migration is done, reducing the time spent with the subtree frozen.
Note: ignore my prior e-mail, some errors occurred ;)
Odair M. Ditkun Jr
Centro de Computação Científica e Software Livre — C3SL
Mestrando em Redes e Sistemas Distribuídos — PPGINF
Bacharel Ciência da Computação — UFPR
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