On 9/18/18 7:32 AM, Dave Chinner wrote: > On Tue, Sep 18, 2018 at 07:46:47AM -0400, Mikulas Patocka wrote: >> I would ask the XFS developers about this - why does mkfs.xfs select >> sector size 512 by default? > > Because the underlying device told it that it supported a > sector size of 512 bytes? Not only that, but it must have told us that it had a /physical/ 512 sector. If it had even said physical/logical 4096/512, we would have chosen 4096. What does please check blockdev --getpbsz --getss /dev/$FOO say at mkfs time? >> If a filesystem created with the default 512-byte sector size is activated >> on a device with 4k sectors, it results in mount failure. > > Yes, it does, but mkfs should also fail when it tries to write 512 > byte sectors to a 4k device, too. ... > I'm betting that the underlying device advertised a logical/physical > sector size of 512 bytes to mkfs, and then adding pmem as the cache > device changed the logical volume from a 512 byte sector device to a > hard 4k sector device. Yup, please check blockdev --getpbsz --getss /dev/$FOO for the devices in question during the course of this testcase. As Dave says, we can't mkfs a device that claims to support 512 bytes IOs and then have that granularity increase. (And going the other way, i.e. making 512 byte IOs non-atomic may break guarantees that journaling relies on). -Eric
