Raid:Creating large raid5 array (over 2TB drive)

	Skill level: Advanced
	The instructions on this page may require deviations from standard procedures. A good understanding of linux and Koozali SME Server is recommended.

This is the initial forum post this howto provide one solution to overcoming current Centos 5 problems with raiding hard disk drives with capacities over 2TB in size.

The purpose of this HOWTO is to create a Raid5 array of greater than 7TB (19TB) using SME Server 8.0, this is intended as a clean installation.

Creating Large Raid5 Array using 4TB drives

	Note:
	due to a limitations in kernel 2.6.18 which is the default kernel of Centos 5 and SME Server 8.0, you can not create Raid5 arrays from drives with a capacity of more than 2TB. This means that the largest size using the standard SME Server 8.0 install is limited to 7.2TB. For those that have and existing array of 7.2TB and need more space you can growing your existing array please follow Howto

In the howto below we will be creating an array using 6x 4TB drives to create a new Raid5 array of 19TB in capacity. Below is the basic hardware details of the computer that were used, these are only a guide.

 - Large case capable of fitting 12 drives - Gigabyte 3D Aurora
 - Main board with 6 SATA 3 ports on board - Gigabyte GA-970A-D3
 - SATA Controller 4 SATA 3 ports on board - Rocket R640L
 - 6x 4TB Hard disk drives - 19TB Array
 - 1x 500MB Hard disk drive - SME Server 8.0 operating system

Before starting the howto below you should have installed SME Server 8.0 on the computer and have run and installed all updates as per a normal server installation. Leave the 6x 4TB drives unplugged until you begin the howto below.

	Warning:
	This howto is intended as a guide to set a new server which has no existing data, do NOT run this on a live server without a backup of that system.

Installing required tools

You will need to install some additionally tools

parted: Parted is a GNU utility, which is used to manipulate the hard disk partitions. Using parted, you can add, delete, and edit partitions and the file systems located on those partitions
xfsprogs: Utilities for managing the XFS filesystem A set of commands to use the XFS filesystem, including mkfs.xfs. XFS is a high performance journaling filesystem which originated on the SGI IRIX platform. It is completely multi-threaded, can support large files and large filesystems, extended attributes, variable block sizes, is extent based, and makes extensive use of Btrees (directories, extents, free space) to aid both performance and scalability.

Install the required tools using the Yum commands below.

yum install parted

yum install xfsprogs

It’s usually a good idea to run… but not required 
Signal-event post-upgrade;
Signal-event reboot;

Partitioning the drives

Now we need to create the partition for the drives using the parted partitioning tool.

parted /dev/sdX
mklabel gpt
unit TB
mkpart primary 0.00TB 4.00TB
print

Remember to set the max size (4.00TB above) to whatever size hard disk drives you are using also you will need to change the device sdX value for each drive in the chain.

Creating the array

Check which md numbers are in use by running the command cat /proc/mdstat select the highest number md number and add one we will us md3.

mdadm --create /dev/md3  --level=raid5 --raid-devices=6 /dev/sda1 /dev/sdb1 /dev/sdc1 /dev/sdd1 /dev/hda1 /dev/hdb1

Change the md3 number to the one you have selected, you will also need to change the number of raid devices and list each of the devices to use in the array.

	Note:
	Be Advised this command will process quickly but will continue to run a re-sync of the RAID array in the background. You can monitor this re-sync by running cat /proc/mdstat, It highly advisable to wait for the re-sync to be completed before proceeding.

Save raid array structure

Next we need to save array structure to the mdadm.conf file in order for the SME Server to continue working with the array on reboot of the system.

mdadm --detail --scan | grep md3 >> /etc/mdadm.conf

Once that command is run it would be a good advisable to view the file, You should only see one new line in the file. It is the then a good idea to create a copy of the mdadm.conf by running the following command

cp /etc/mdadm.conf /etc/mdadm.conf.bak

Keep this file permanently as it is possible in the future something may occur on your SME Server to cause the mdadm.conf file to be trashed or reset, in that case you can use this backup file to rewrite your required raid information.

Create your lvm partition

When using the vgcreate command use a good name for your partition, I have just used vg_DATA and lv_DATA.

 pvcreate /dev/md3
 vgcreate vg_DATA /dev/md3
 lvcreate --name lv_DATA -l 100%FREE vg_DATA

	Note:
	I have noticed these commands do take a while, be patience..

Format your new Partition and testing

Run the following

mkfs.xfs /dev/vg_DATA/lv_DATA

If you want to be sure everything went ok you can run a file check on the new LVM once the format is complete.

xfs_check /dev/vg_DATA/lv_DATA

	Note:
	I found that I could not use EXT3 or EXT4 based file systems due to problems with the block sizes and my 20TB setup there may be work-around for this, but I didn’t find anything solid so instead I decided use XFS file system as it does what I need it too.

Mount your new partition to a directory

Finally open /etc/fstab and edit the bottom line to mount the new area be sure to leave a new line feed at the bottom, and use proper spacing.

For Example in my file I entered

/dev/vg_DATA/lv_DATA	/TESTFOLDER	XFS	defaults	0 0

You trigger a remount by using

mount –a

You can also check whether it has been successful mounted easily by running it should list your mount location and size in use.

df -h

This setup in /etc/fstab should be maintained when updates or upgrades are conducted however if you want a more definite solution I would advise reading up on templates in SME Server.