Filesystem

Journal type

  • ordered: It is the default mode. All data is forced directly out to the main file system prior to its meta-data being committed to the journal.
  • writeback: Data ordering is not preserved, data may be written into the main file system after its metadata has been committed to the journal. This is rumored to be the highest-throughput option. It guarantees internal file system integrity, however it can allow old data to appear in files after a crash and journal recovery.
  • journal: All data is committed into the journal prior to being written into the main file system.

Mount options

defaults = (rw, suid, dev, exec, auto, nouser, async, and relatime)

I/O scheduler

  • anticipatory (RHEL 4-5)
  • noop
  • deadline
  • cfq

Commands

  • Display the scheduler for disk: cat /sys/block/<disk>/queue/scheduler
  • Change the scheduler online: echo deadline > /sys/block/<disk>/queue/scheduler
  • Change the scheduler globally (or write udev rules):

vi /etc/grub.conf

kernel.... elevator=deadline

reboot

tuned

  • Install the package: yum install tuned; chkconfig tuned on; /etc/init.d/tuned start
  • List all available profiles: tuned-adm list
  • Display the active profile: tuned-adm active
  • Change the profile (conf file - /etc/ktune.d/tunedadm.conf): tuned-adm profile virtual-host

Commands

  • Check mount options: cat /proc/mounts
  • Add a new partition in RHEL6 without reboot:

partprobe was commonly used in RHEL 5 to inform the OS of partition table changes on the disk. In RHEL 6, it will only trigger the OS to update the partitions on a disk that none of its partitions are in use (e.g. mounted). If any partition on a disk is in use, partprobe will not trigger the OS to update partitions in the system because it is considered unsafe in some situations.

So in general we would suggest:

  1. Unmount all the partitions of the disk before modifying the partition table on the disk, and then run partprobe to update the partitions in system.
  2. If this is not possible (e.g. the mounted partition is a system partition), reboot the system after modifying the partition table. The partitions information will be re-read after reboot.

If a new partition was added and none of the existing partitions were modified, consider using the partx command to update the system partition table. Do note that the partx command does not do much checking between the new and the existing partition table in the system and assumes the user knows what they are are doing. So it can corrupt the data on disk if the existing partitions are modified or the partition table is not set correctly. So use at one's own risk.

partx -l /dev/sdb
partx -v -a /dev/sdb
ls /dev/sdb*                      (sdb1 and sdb2 should be visible)