Tuesday, January 10, 2017

Making Logical Disks from Physical Hard Disks (Configuring RAID Controller)

This is probably the first thing you will need to do after you bought a used server. My server is Dell PowerEdge 2970 and it had 8 physical hard disks inside when I bought it.
(4x73GB + 4x600GB)

Which means all the physical disks have 2.69 TB in total. But actual useful space is lower than that. It depends on how we design our storage to be in terms of high availability, fault tolerance, speed and performance.. I'll explain it now.. Above 8 hard disks can be combined in several ways to make logical hard disks.  After all, the logical hard disks are the disks which can be seen by Operating Systems which are going to be installed later on this server. (Do not misunderstand this with partitions).
Those combining methods are called RAID levels and this combining is done through the RAID controller in the server. This server uses PERC 5/i as the Configuration Utility.

Understanding RAID Levels

RAID is the abbreviated term for Redundant Array of Independent Disks.

Basically what we do here is that we take several physical hard disks and group them to create logical hard disks. So we can choose which RAID level (combining method) to be used in our storage based on our requirements. Each type has advantages and disadvantages. Some methods are good for high availability while some are better for speed etc.

Following are the most common..

RAID level 0 - 
No redundant / back up.. It only write data in 2 disks at the same time. Half of data in one disk and the other half in the other disk. If one disk become faulty you don't have a backup. All the array fails. Advantage is the speed..

RAID level 1 -
This method stores same data in 2 disks. So if one disk fails you have a back up. Disadvantage is you can use only half of your total disk space for your storage..

RAID level 5 - (Most Common Implementation, Better for Overall Performance)
You need to have 3 or more disks for this method. Data is not duplicated, works like level 0 RAID but it uses a parity for data recovery in a case of a hard disk failure. So this method is fast and reliable while you can use 3/4 of your total disk space to store data. Using a Hot Spare drive (dedicated drive to act as a recovery disk in a case of a disk failure) will be a good option with this level of RAID. The size of the Hot Spare disk must be at least equal to the largest physical disk in the array..

RAID level 10 - 
Combination of RAID 1 and RAID 0. Again has a disadvantage of loosing a half of total disk space..

How I Planned..

I am chose RAID level 5 because the availability matters for me. The thing is I could create a one logical hard disk by combining all 8 physical disks. but because there are 2 sizes of hard disks with me, it will not be a good solution. Because they don't work well just like that if the sizes are different. I really tried to do that once but the maximum logical hard disk I could create was about 450 GB in size with RAID level 5.

So to get maximum out of the drives I have with high availability, I designed it to be like this..
















So as you can see, I am going to create 2 logical disks because I have 2 types in sizes.
Logical disk 1 will contain three 73 GB hard disks with a one 73 GB Hot Spare disk..
Logical disk 2 will contain three 600 GB hard disks with a one 600 GB Hot Spare disk..

Configuring RAID Controller

Booted up and read the outputs to find the key combination to break into the RAID controller interface. It will show something like Press Ctrl+R to Run Configuration Utility


(click on the images to view in full size)



I am deleted all the RAIDs configured by the previous owner.

Highlighted the Controller 0 by arrow keys and delete Foreign Configurations (disks configured for other outside systems) if there are any..


Then selected and hit Enter to Reset Config..

Again highlighted the Controller 0 and selected Create New VD..

VD stands for Virtual Disk.. (Logical Disk)

Using Tab & Space  you can select the RAID levels, hard disks you want to put in a single logical array.  You can see my selections and all the settings for my 1st VD. VD size is auto generated to the maximum value and I gave the name VD-01. In advanced settings, I selected the write policy to be "write through" which is the fastest way.

Also selected to configure Hot Spare.
Hit Ok..

Now it asked which disk to be the Hot Spare. I selected the remaining 73 GB one and Hit Ok..







Now created the 2nd VD just like the 1st one..


Total size for VD-02 is like about 1.14 TB..









Selected the remaining 600 GB disk to be the Hot Spare for the VD-02.









Now the setup is configured but had to wait a long time till the controller initialize the virtual disks..

After the 1st one is initialized, it will go to the 2nd one..
After the initialization is completed, hit Escape and it asked to hit Alt + Ctrl + Del to restart the system.







You can see the logical disks I created in the final capture as it appeared during an OS installation..
Now it's like  2 hard disks of 145.5 GB and 1.2 TB..










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