drbd: prepare for new striped layout of activity log
Introduce two new on-disk meta data fields: al_stripes and al_stripe_size_4k The intended use case is activity log on RAID 0 or similar. Logically consecutive transactions will advance their on-disk position by al_stripe_size_4k 4kB (transaction sized) blocks. Right now, these are still asserted to be the backward compatible values al_stripes = 1, al_stripe_size_4k = 8 (which amounts to 32kB). Also introduce a caching member for meta_dev_idx in the in-core structure: even though it is initially passed in in the rcu-protected disk_conf structure, it cannot change without a detach/attach cycle. Signed-off-by: NPhilipp Reisner <philipp.reisner@linbit.com> Signed-off-by: NLars Ellenberg <lars.ellenberg@linbit.com> Signed-off-by: NJens Axboe <axboe@kernel.dk>
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