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
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