On 9/18/18 9:16 AM, Eric Sandeen wrote: > On 9/18/18 9:09 AM, Mikulas Patocka wrote: >> >> >> On Tue, 18 Sep 2018, Eric Sandeen wrote: >> >>> 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? >> >> On SSDs, physical sector size is not detectable - the ATA and NVME >> standards allows reporting physical sector size, but some SSD vendors >> report this as 512-bytes despite the fact that the SSD has 4k sectors >> internally. > > There's a difference between "detecting" and "observing what the > device reports." > > All we have to go on is the geometry reported by the device. > > # cat /sys/block/sdc/device/model > Samsung SSD 850 > # blockdev --getpbsz --getss /dev/sdc > 512 > 512 > > If the device lies to us, there's nothing to be done about it. > >> I tested 5 SSDs (Samsung SSD 960 EVO NVME, KINGSTON SKC1000240G NVME, >> Samsung SSD 850 EVO SATA, Crucial MX100 SATA, Intel 520 SATA) - all of >> them have 4k sectors internally (i.e. the SSDs have higher IOPS for 4k >> writes than for 2k writes), but only the Crucial SSD reports 4096 in >> /sys/block/*/queue/physical_block_size. Intel and Samsung report 512. See also https://www.intel.com/content/www/us/en/support/articles/000006392/memory-and-storage.html -Eric
