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c4f4t0r
Asked: 2014-06-14 03:13:04 +0800 CST

ext3/ext4 physical block size view

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I'm using a suse 11 server with xfs and using "xfs_info /srv" command i seen this.

xfs_info /srv/
meta-data=/dev/mapper/vg01-srvvol isize=256    agcount=38, agsize=1964032 blks
     =                       sectsz=512   attr=2
data     =                       bsize=4096   blocks=73367552, imaxpct=25
     =                       sunit=0      swidth=0 blks
naming   =version 2              bsize=4096   ascii-ci=0
log      =internal               bsize=4096   blocks=3836, version=2
     =                       sectsz=512   sunit=0 blks, lazy-count=1
realtime =none                   extsz=4096   blocks=0, rtextents=0

So i think xfs knows the size of underline disk sectsz, but I'm using now a disk with sectsz of 512 bytes, but my question is, how can find this kind of information using ext3/ext4 filesystem?

Because i would like to try to use a new disk with sectsz of 4096 and be sure, ext3/ext4 uses the underline sectsz.

This is the output of xfs_info using one new ssd with physical block size 4096:

xfs_info /dev/mapper/vg00-logvol
meta-data=/dev/mapper/vg00-logvol isize=256    agcount=16, agsize=7144576 blks
         =                       sectsz=4096  attr=2, projid32bit=0
data     =                       bsize=4096   blocks=114313216, imaxpct=25
         =                       sunit=0      swidth=0 blks
naming   =version 2              bsize=4096   ascii-ci=0
log      =internal               bsize=4096   blocks=55817, version=2
         =                       sectsz=4096  sunit=1 blks, lazy-count=1
realtime =none                   extsz=4096   blocks=0, rtextents=0
linux

3 Answers

  1. $ sudo tune2fs -l /dev/vda1 
tune2fs 1.42.8 (20-Jun-2013)
Filesystem volume name:   <none>
...
Free inodes:              127696
First block:              1
Block size:               1024
Fragment size:            1024
Reserved GDT blocks:      256
Blocks per group:         8192
...
    • 6

  2. First, find the underlying dm device:

    ls -l /dev/mapper/vg01-srvvol

    Example output:

    lrwxrwxrwx 1 root root 7 Jan 28 14:32 /dev/mapper/vg01-srvvol -> ../dm-0

    Take the dm-0, dm-1, etc and see here:

    cat /sys/block/dm-0/queue/physical_block_size
    • 2

  3. The only reliable way to determine the real physical block size is by querying the disk directly with hdparm:

    hdparm -I /dev/sdX | grep Physical

    All linux tools like parted, tune2fs, fdisk, also the kernel (via the value provided in /proc) output 512 Bytes for disks I have which are denoted 4K by hdparm. (5 HDDs tested, with two being 4K ones.)

    • 1