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Hey Andy, I would rather see performance figures for these setups: A) btrfs with 2 (or more) hard drives and one SSD in writeback bcache configuration (unsafe against failure of the ssd): +-----------------------------+ | btrfs raid 1 /mnt | +--------------+--------------+ | /dev/Bcache0 | /dev/Bcache1 | +--------------+--------------+ | bcache writeback Cache | | /dev/sdk1 | +--------------+--------------+ | Data | Data | | /dev/sdv1 | /dev/sdw1 | +--------------+--------------+
Doing that, you loose the protection of raid1 redundancy: now there is a single point of failure /dev/sdk1. Writeback is even more dangerous...
B) btrfs with 2 (or more) hard drives and two SSD's in dm-raid 1 writeback bcache configuration (unsafe against corruption of any of the ssd's): +-----------------------------+ | btrfs raid 1 /mnt | +--------------+--------------+ | /dev/Bcache0 | /dev/Bcache1 | +--------------+--------------+ | bcache writeback Cache | | /dev/dm0 | +--------------+--------------+ | 2x SSD in mdadm raid 1 | | /dev/sdk1 /dev/sdl1 | +--------------+--------------+ | Data | Data | | /dev/sdv1 | /dev/sdw1 | +--------------+--------------+ C) Full stack: btrfs with 2 (or more) hard drives and two identical SSD's in dm-raid 1 with dm-integrity writeback bcache configuration (safe against any failed drive): +-----------------------------+ | btrfs raid 1 /mnt | +--------------+--------------+ | /dev/Bcache0 | /dev/Bcache1 | +--------------+--------------+ | bcache writeback Cache | | /dev/dm0 | +--------------+--------------+ | 2 x dm-integrity devices | | in mdadm raid 1 | +--------------+--------------+ | SSD hosting | SSD hosting | | dm-integrity | dm-integrity | | /dev/sdk1 | /dev/sdl1 | +--------------+--------------+ | Data | Data | | /dev/sdv1 | /dev/sdw1 | +--------------+--------------+ D) Full stack: btrfs with 2 (or more) hard drives and two SSD's (one slow, and one very fast) in dm-raid 1 with dm-integrity writeback bcache configuration (safe against any failed drive): +-----------------------------+ | btrfs raid 1 /mnt | +--------------+--------------+ | /dev/Bcache0 | /dev/Bcache1 | +--------------+--------------+ | bcache writeback Cache | | /dev/dm0 | +--------------+--------------+ | 2 x dm-integrity devices | | in mdadm raid 1 | +--------------+--------------+ | SSD hosting | SSD hosting | | dm-integrity | dm-integrity | | /dev/sdk1 | /dev/sdl1 | +--------------+--------------+ | Data | Data | | /dev/sdv1 | /dev/sdw1 | +--------------+--------------+ In all these setups, the performance of the hard drives is irrelevant, because the speed of the setups comes from the bcache SSD. Cheers, Cedric --- Take your mailboxes with you. Free, fast and secure Mail & Cloud: https://www.eclipso.eu - Time to change!
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