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? > 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. > On Tue, 11 Sep 2018, David Teigland wrote: > > > Hi Mikulas, > > > > Am I doing something wrong below or is there a bug somewhere? (I could be > > doing something wrong in the lvm activation code, also.) > > Thanks > > > > > > [root@null-05 ~]# lvs foo > > LV VG Attr LSize > > fast foo -wi------- 32.00m > > main foo -wi------- 200.00m > > > > [root@null-05 ~]# lvchange -ay foo/main > > > > [root@null-05 ~]# mkfs.xfs /dev/foo/main > > meta-data=/dev/foo/main isize=512 agcount=4, agsize=12800 blks > > = sectsz=512 attr=2, projid32bit=1 > > = crc=1 finobt=0, sparse=0 > > data = bsize=4096 blocks=51200, imaxpct=25 > > = sunit=0 swidth=0 blks > > naming =version 2 bsize=4096 ascii-ci=0 ftype=1 > > log =internal log bsize=4096 blocks=855, version=2 > > = sectsz=512 sunit=0 blks, lazy-count=1 > > realtime =none extsz=4096 blocks=0, rtextents=0 > > > > [root@null-05 ~]# mount /dev/foo/main /mnt > > [root@null-05 ~]# cp /root/pattern* /mnt/ > > [root@null-05 ~]# umount /mnt > > [root@null-05 ~]# lvchange -an foo/main > > > > [root@null-05 ~]# lvconvert --type writecache --cachepool fast foo/main > > Logical volume foo/main now has write cache. > > > > [root@null-05 ~]# lvs -a foo -o+devices > > LV VG Attr LSize Origin Devices > > [fast] foo -wi------- 32.00m /dev/pmem0(0) > > main foo Cwi------- 200.00m [main_wcorig] main_wcorig(0) > > [main_wcorig] foo -wi------- 200.00m /dev/loop0(0) Yeehaw! 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. If so, this is a dm-cache bug. Filesystems don't support changing the logical/physical sector sizes of the block device dynamically. Filesystems lay out the filesystem structure at mkfs time based on the assumption that the sector size of the block device is fixed and will never change for the life of that filesystem. Indeed, if the sector size of the block device is not fixed and can change dynamically, then the block device also violates the assumptions that the filesystem journalling algorithms make about the atomic write size of the underlying device.... Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx
