Hi, I've been using a btrfs volume in a NFS server for some time, based in iscsi storage with 4k sectors. Due to problems with NFS I've decided to drop iscsi and make the iscsi target server (standard x86 box with raid drive) a secondary NFS server. This requires mounting the btrfs volume directly on the new NFS server. The raid array (linux md raid 6) reports the raid drive as a 512b sector size drive. Mounting the btrfs volume fails with an "already mounted" error message; running "btrfs check" also does not recognize the volume. "btrfs fi show" shows the correct information about the volume, "btrfs-show-super" also prints the correct information from the superblock. It also indicates that the volume assumes 4k sectors. I was finally able to mount the volume using a loopback device. A subsequent scrub run show no errors at all, so the volume itself is ok. The questions are: - Is btrfs dependent on the sector size of the underlying storage? - Is it possible to change the sector size, e.g. after migrating a volume to a different storage? Output of btrfs-show-super: superblock: bytenr=65536, device=/dev/vg00/secondary_nas --------------------------------------------------------- csum 0xb9f1cb2f [match] bytenr 65536 flags 0x1 magic _BHRfS_M [match] fsid 41eea530-05a9-4af4-9c23-a12d99ec64d0 label secondary generation 108373 root 13237056634880 sys_array_size 129 chunk_root_generation 108362 root_level 1 chunk_root 13272016519168 chunk_root_level 1 log_root 0 log_root_transid 0 log_root_level 0 total_bytes 32985348833280 bytes_used 13287498846208 sectorsize 4096 nodesize 16384 leafsize 16384 stripesize 4096 root_dir 6 num_devices 1 compat_flags 0x0 compat_ro_flags 0x0 incompat_flags 0x61 csum_type 0 csum_size 4 cache_generation 108373 uuid_tree_generation 108373 dev_item.uuid 3b80d2e0-3cd7-46fd-b9be-f0c318e0ec75 dev_item.fsid 41eea530-05a9-4af4-9c23-a12d99ec64d0 [match] dev_item.type 0 dev_item.total_bytes 32985348833280 dev_item.bytes_used 13315547856896 dev_item.io_align 4096 dev_item.io_width 4096 dev_item.sector_size 4096 dev_item.devid 1 dev_item.dev_group 0 dev_item.seek_speed 0 dev_item.bandwidth 0 dev_item.generation 0 I can live with the current setup for the moment, but using the loopback device may have an impact on performance, so I'm looking for the easiest way to mount the volume without any workaround Best regards, Burkhard Linke -- Dr. rer. nat. Burkhard Linke Bioinformatics and Systems Biology Justus-Liebig-University Giessen 35392 Giessen, Germany Phone: (+49) (0)641 9935810 -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html