On Sun, 30 Nov 2014 12:11:47 +0100 Gour <g...@atmarama.net> wrote: > However, I wonder if there are some 'cons' in having raid-1 partition > under mdadm and not using native mirroring capabilities of btrfs fs?
Pros: * mdadm RAID has much better read balancing; Btrfs reads are satisfied from what's in effect a random drive (PID-based balancing of threads to drives), mdadm reads from the less-loaded drive. Also mdadm has a way to specify some RAID1 array members as to be never used for reads if at all possible ("write-mostly"), which helps in RAID1 of HDD and SSD. * mdadm RAID has much better write submission; In my experience [1] Btrfs RAID1 on heavy write operations first writes to one drive, then to another. The whole process takes up to 2x longer than with a single drive. On the other hand mdadm writes to both drives simultaneously. [1] https://www.mail-archive.com/linux-btrfs@vger.kernel.org/msg34103.html Con: * You only get the ability to recover from a checksum failure with Btrfs RAID1, not with mdadm RAID1 (see Russell's reply). -- With respect, Roman -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html