mounting ext4 fs with block size of 65536

Question

I am doing some benchmarking on EXT4 performance on Compact Flash media.

I have created an ext4 fs with block size of 65536. however I can not mount it on ubuntu-10.10-netbook-i386. (it is already mounting ext4 fs with 4096 bytes of block sizes)

According to my readings on ext4 it should allow such big block sized fs. I want to hear your comments.

root@ubuntu:~# mkfs.ext4 -b 65536  /dev/sda3
Warning: blocksize 65536 not usable on most systems.
mke2fs 1.41.12 (17-May-2010)
mkfs.ext4: 65536-byte blocks too big for system (max 4096)
Proceed anyway? (y,n) y
Warning: 65536-byte blocks too big for system (max 4096), forced to continue
Filesystem label=
OS type: Linux
Block size=65536 (log=6)
Fragment size=65536 (log=6)
Stride=0 blocks, Stripe width=0 blocks
19968 inodes, 19830 blocks
991 blocks (5.00%) reserved for the super user
First data block=0
1 block group
65528 blocks per group, 65528 fragments per group
19968 inodes per group

Writing inode tables: done
Creating journal (1024 blocks): done
Writing superblocks and filesystem accounting information: done

This filesystem will be automatically checked every 37 mounts or
180 days, whichever comes first.  Use tune2fs -c or -i to override.



root@ubuntu:~# tune2fs -l /dev/sda3
tune2fs 1.41.12 (17-May-2010)
Filesystem volume name:   <none>
Last mounted on:          <not available>
Filesystem UUID:          4cf3f507-e7b4-463c-be11-5b408097099b
Filesystem magic number:  0xEF53
Filesystem revision #:    1 (dynamic)
Filesystem features:      has_journal ext_attr resize_inode dir_index
filetype extent flex_bg sparse_super large_file huge_file uninit_bg
dir_nlink extra_isize
Filesystem flags:         signed_directory_hash
Default mount options:    (none)
Filesystem state:         clean
Errors behavior:          Continue
Filesystem OS type:       Linux
Inode count:              19968
Block count:              19830
Reserved block count:     991
Free blocks:              18720
Free inodes:              19957
First block:              0
Block size:               65536
Fragment size:            65536
Blocks per group:         65528
Fragments per group:      65528
Inodes per group:         19968
Inode blocks per group:   78
Flex block group size:    16
Filesystem created:       Sat Feb  5 14:39:55 2011
Last mount time:          n/a
Last write time:          Sat Feb  5 14:40:02 2011
Mount count:              0
Maximum mount count:      37
Last checked:             Sat Feb  5 14:39:55 2011
Check interval:           15552000 (6 months)
Next check after:         Thu Aug  4 14:39:55 2011
Lifetime writes:          70 MB
Reserved blocks uid:      0 (user root)
Reserved blocks gid:      0 (group root)
First inode:              11
Inode size:               256
Required extra isize:     28
Desired extra isize:      28
Journal inode:            8
Default directory hash:   half_md4
Directory Hash Seed:      afb5b570-9d47-4786-bad2-4aacb3b73516
Journal backup:           inode blocks


root@ubuntu:~# mount -t ext4 /dev/sda3 /mnt/
mount: wrong fs type, bad option, bad superblock on /dev/sda3,
      missing codepage or helper program, or other error
      In some cases useful info is found in syslog - try
      dmesg | tail  or so

Answer 1

The max ext4 block size is still limited by the page size of the kernel/cpu. Your page size is 4k and so the max ext4 block size is 4k.

Answer 2

I'd say use 4kb blocks for compatibility and use extents and stripe stride-width options on create/mount to get block allocations in accordance with erase block size of your flash media.

Make sure also that partition is aligned to this erase block size too!