fsck - check and repair a Linux file system

       The exit code returned by fsck is the sum of the following conditions:
            0    - No errors
            1    - File system errors corrected
            2    - System should be rebooted
            4    - File system errors left uncorrected
            8    - Operational error
            16   - Usage or syntax error
            32   - Fsck canceled by user request
            128  - Shared library error

Improve Faster IO for your filesystem by chaning the READ AHEAD Value

[root@test oracle]# df -Th /oracle
Filesystem    Type    Size  Used Avail Use% Mounted on
/dev/mapper/oracle-oracle_lv
              ext4   1008M   34M  924M   4% /oracle

[root@test oracle]# time dd if=/oracle/test of=/tmp/test count=500 bs=1M
500+0 records in
500+0 records out
524288000 bytes (524 MB) copied, 6.2385 s, 84.0 MB/s

real    0m6.249s
user    0m0.001s
sys     0m1.886s
[root@test oracle]#

[root@test oracle]# blockdev --report /dev/sdb
RO    RA   SSZ   BSZ   StartSec            Size   Device
rw   256   512  4096          0      5368709120   /dev/sdb
[root@test oracle]#


I changed the read ahead value from 256 to 1024:

[root@test ~]#  blockdev --setra 1024 /dev/sdb
[root@test ~]# blockdev --getra /dev/sdb
1024
[root@test ~]# blockdev --report /dev/sdb
RO    RA   SSZ   BSZ   StartSec            Size   Device
rw  1024   512  4096          0      5368709120   /dev/sdb
[root@test ~]#

[root@test oracle]# time dd if=/oracle/test of=/tmp/test count=500 bs=1M
500+0 records in
500+0 records out
524288000 bytes (524 MB) copied, 3.79428 s, 138 MB/s

real    0m3.819s
user    0m0.003s
sys     0m1.589s
[root@test oracle]#


The read performace has improved from 6.2 Sec to 3.8 Sec. Faster IO.

Currently set to and Block device in lvdisplay ?

[root@test ~]# lvdisplay /dev/hits/hits1
  --- Logical volume ---
  LV Name                /dev/hits/hits1
  VG Name                hits
  LV UUID                W7uUkN-WAIf-MrY7-u7oE-x9uy-AegG-WYATjI
  LV Write Access        read/write
  LV Status              available
  # open                 0
  LV Size                1.00 GiB
  Current LE             256
  Segments               1
  Allocation             inherit
  Read ahead sectors     auto
  - currently set to     256
  Block device           253:0

[root@test ~]#

Most of us would wonder few things with the output of # lvdisplay especially the bottom two lines.
currently set to and Block device.

Block device:

Block Devices refers to the DM (Device Multipath) Associated with the logical volume.

[root@test ~]# dmsetup ls --tree
hits-hits1 (253:0)
 └─ (8:16)

[root@test dev]# ls -l | grep -i "253"

brw-rw----. 1 root disk    253,   0 Jul  4 17:50 dm-0

[root@test dev]#

dm-0 is the device multipath associated with the logical volume hits1.

How to check the Block Size and Sector Size of HDD in Linux ?

[root@test ~]# blockdev --report /dev/sdb
RO    RA   SSZ   BSZ   StartSec            Size   Device
rw   256   512  4096          0      5368709120   /dev/sdb
[root@test ~]#

RA : Read Ahead.

SSZ : Sector Size.

BSZ : Block Size.

Size : Size of the disk.

Available commands:

        --getsz                        get size in 512-byte sectors

        --setro                        set read-only

        --setrw                        set read-write

        --getro                        get read-only

        --getss                        get logical block (sector) size

        --getpbsz                      get physical block (sector) size

        --getiomin                     get minimum I/O size

        --getioopt                     get optimal I/O size

        --getalignoff                  get alignment offset

        --getmaxsect                   get max sectors per request

        --getbsz                       get blocksize

        --setbsz BLOCKSIZE             set blocksize

        --getsize                      get 32-bit sector count

        --getsize64                    get size in bytes

        --setra READAHEAD              set readahead

        --getra                        get readahead

        --setfra FSREADAHEAD           set filesystem readahead

        --getfra                       get filesystem readahead

        --flushbufs                    flush buffers

        --rereadpt                     reread partition table