I created a multi-device btrfs filesystem across two drives: 80 GB SATA 2.5 inch drive (sdb) 120 GB PATA 3.5 inch drive (sdd) If I copy a decent-sized file to the filesystem, there are "bio too big" messages in dmesg, and I get read errors (along with ''btrfs csum failed'') when trying to read them again. The process writing the files is unaware the data was not saved correctly. The exact message while writing is this (with the 1024 sometimes varying): bio too big device sdd1 (1024 > 256) The 120 GB drive (sdd) works fine for single-device btrfs, so my guess is that btrfs trying to use one set of parameters for all devices on a filesystem and is therefore submitting out-of-spec write requests to the older 120 GB PATA drive. As I understand it, the relevant parameters are these: $ cat /sys/block/sdb/queue/max_sectors_kb 512 $ cat /sys/block/sdd/queue/max_sectors_kb 128 Is this a known issue? Is it specifically a btrfs issue? dmesg is attached.