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.
Note: ignore my prior e-mail, some errors occurred ;)
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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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