Install ZFS and create zpool on Centos 6.6

Install ZFS and create zpool on Centos 6.6

Assuming this is a clean, up to date install of CentOS you will need to install EPEL and ZFS from RPM, this is the simplest way to get ZFS today:

yum localinstall --nogpgcheck https://download.fedoraproject.org/pub/epel/6/x86_64/epel-release-6-8.noarch.rpm

yum localinstall --nogpgcheck http://archive.zfsonlinux.org/epel/zfs-release.el6.noarch.rpm

yum install kernel-devel zfs

You can now load the ZFS module:

modprobe zfs

After running the above command you should have seen a list of loaded modules from ZFS.

# lsmod | grep -i zfs

zfs                  2179437  3

zcommon                47120  1 zfs

znvpair                80252  2 zfs,zcommon

spl                    89796  3 zfs,zcommon,znvpair

zavl                    6784  1 zfs

zunicode              323046  1 zfs

You should now make sure the module is loaded persistently on boot. We need to make a new file and add a script to it.

vi /etc/sysconfig/modules/zfs.modules

Add the following code:

#!/bin/sh

if [ ! -c /dev/zfs ] ; then

        exec /sbin/modprobe zfs >/dev/null 2>&1

fi

Make this file executable:

chmod +x /etc/sysconfig/modules/zfs.modules

Now reboot and make sure everything loaded

reboot

After reboot run lsmod again and make sure modules are loaded

# lsmod | grep -i zfs

zfs                  2179437  3

zcommon                47120  1 zfs

znvpair                80252  2 zfs,zcommon

spl                    89796  3 zfs,zcommon,znvpair

zavl                    6784  1 zfs

zunicode              323046  1 zfs

Now we need to set up a zpool. In ZFS terms, I will be stripping two mirrors, or better known as raid10. First let’s check the disks we will use for any mbr or partition info. If we find that lets remove it. NOTE** This will erase all data on the disks you do this to.

fdisk –l | grep GB

For me the drives I will be using are /dev/sdb through /dev/sde. I have old information on the drives from an old mdadm raid array, so I will remove it. I will show just /dev/sdb on this example. Make sure to do this to all the drives that you want to use, if they have old array data on them.

fdisk /dev/sdb

Command (m for help): p

After reviewing the information, and you still want to remove it:

Command (m for help): d

Selected partition 1

Command (m for help): w

Now do this for all the other disk you will use in your array.

Just to be sure let’s zero out the first 1MB of data on the drive to insure the removal of MBR and partition data

dd if=/dev/zero of=/dev/sdb bs=1M count=1

Remember do this for all the other disk you will use in your array.

Next I setup the RAID (using a name of myriad. You can use what you like):

zpool create myraid mirror -f /dev/sdb /dev/sdc mirror /dev/sdd /dev/sde

Now make sure it was created

# zpool status

  pool: myraid

 state: ONLINE

  scan: none requested

config:

        NAME        STATE     READ WRITE CKSUM

        myraid      ONLINE       0     0     0

          mirror-0  ONLINE       0     0     0

            sdb     ONLINE       0     0     0

            sdc     ONLINE       0     0     0

          mirror-1  ONLINE       0     0     0

            sdd     ONLINE       0     0     0

            sde     ONLINE       0     0     0

errors: No known data errors

Check it is mounted

mount | grep zfs

df -h | grep myriad

If you don’t see it mounted try

zfs mount myriad

Add ZFS to auto mount /myraid with boot if wanted

echo "zfs mount myraid" >> /etc/rc.local

That’s it. Other things you can do is add SSD caching, compression, deduping, etc. Know what these do before using them though J

zpool add myraid cache sde2

zfs set compression=on myraid

zfs set dedup=on myraid
zfs get compressratio myraid
zfs set compression=lz4 myraid
zfs get all myraid
zfs create -V 10G myraid/name_of_volume 
zfs destroy myraid/name_of_volume


Replace failed drive


# zpool offline raid0 sdb


Take server down and replace physical drive. Use parted to get a partition back on drive.


# zpool online raid0 sdb
# zpool replace raid0 sdb
# zpool status tank

If you move your drives/pool to another system you can use


# zpool import -f tank
To speed things up

# zfs set sync=disabled tank

Read below before disabling though

sync=standard
  This is the default option. Synchronous file system transactions
  (fsync, O_DSYNC, O_SYNC, etc) are written out (to the intent log)
  and then secondly all devices written are flushed to ensure
  the data is stable (not cached by device controllers).

sync=always
  For the ultra-cautious, every file system transaction is
  written and flushed to stable storage by a system call return.
  This obviously has a big performance penalty.

sync=disabled
  Synchronous requests are disabled.  File system transactions
  only commit to stable storage on the next DMU transaction group
  commit which can be many seconds.  This option gives the
  highest performance.  However, it is very dangerous as ZFS
  is ignoring the synchronous transaction demands of
  applications such as databases or NFS.
  Setting sync=disabled on the currently active root or /var
  file system may result in out-of-spec behavior, application data
  loss and increased vulnerability to replay attacks.
  This option does *NOT* affect ZFS on-disk consistency.
  Administrators should only use this when these risks are understood.