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ubuntu - RAID 1+0 vs RAID 0+1




I went with some advice I was given from someone I know to go with a RAID setup for this server I ordered. The specs are below. I plan on using this server to host multiple sites in a PHP/MySQL environment and an SVN repository in Ubuntu Server. I'd like to have a setup where the primary drive is mirrored so that in the event of failure on a drive the server could just use the other pair of drives.



I'm reading on wikipedia about raid setups and I see RAID 0-5, but don't see a 10 listed on wikipedia. Perhaps I'm just not sure what I'm looking for, to be honest I've never used anything RAID.



On-Board Intel ESB2 RAID controller - 0,1,5,10 SATA RAID



Manufacturer: SuperMicro
Model / Part Number: 6015P-TR
Processor(s): Dual (2x) Intel Xeon 2GHz 5130 Dual Core 64-Bit Processors - 4MB Cache, 1333MHz FSB
Memory: 4GB RAM (4x 1GB PC2-5300) - 8 slots on motherboard

Hard Drive(s): Four (4) Hitachi 500GB 7200RPM SATA Hard Drives
Optical Drive: DVD-ROM
Floppy Drive: Included
Network Interface: Dual 10/100/1000 Gigabit Ethernet
RAID: On-Board Intel ESB2 RAID controller - 0,1,5,10 SATA RAID
Power Supplies: 2 (Redundant) - 700W each
Form Factor: Rack Mount - 1U


I'm not sure the best route to take with RAID for what I'm looking for as I'm totally new to it.






update



At this point, when I select RAID10 from the raid controller and go into Ubuntu server installation it shows 2 separate 500GB drives instead of a single 1 TB drive. Ubuntu is not giving me any RAID options duration installation.



I'm thinking I'm just going to install everything on one of those 500 GB drives for the server, then have all my site's data on the other drive.



I need to get moving on this server, I can't spend weeks working out RAID issues.



Answer



The idea of most RAID levels is to provide better reliability or speed for arrays of disks using a combination of the below methods:




  • striping - splits data speed-efficiently across two or more disks +speed

  • mirroring - copies the data onto two or more disks -capacity +reliability

  • parity - a separate disk(s) to verify the data on the other disks is correct +reliability



You have to decide what's most important for you, capacity, reliability, or speed.




Raid 1+0



The official name for RAID 10 is RAID 1+0. Raid 1+0 is a good compromise between speed and reliability as it combines striping and mirroring. Using Raid 1+0, you will have 1TB of space.



How a RAID 1+0 hardware controller works:



+-----------------------------------------------------+
|                                                     |    :
|  500GB          500GB        500GB          500GB   |    :

|    |              |            |              |     |    :
|    +-500GB-MIRROR-+            +-500GB-MIRROR-+     |    : RAID Controller
|           |                           |             |    :
|           +---------1TB-STRIPE--------+             |    :
|                         |                           |    :
+-------------------------|---------------------------+
                          |
+-------------------------|---------------------------+
|                         |                           |    :
|                  OPERATING SYSTEM                   |    :

|                         |                           |    : Software
|                    APPLICATION                      |    :
|                                                     |    :
+-----------------------------------------------------+


It is important to understand that, with a RAID controller, the operating system knows nothing about RAID or multiple disks, it will merely see a plain, single hard drive. All hardware-controlled RAID configuration must be done through the BIOS.



Redundancy: RAID 1+0 vs RAID 0+1




RAID 0+1 is effectively the same thing as RAID 1+0, just the other way round:



                 RAID 1+0              ¡             RAID 0+1              
                                       |                                   
        [#]      [#]   [#]      [#]    |    [#]      [#]   [#]      [#]    
         |        |     |        |     |     |        |     |        |     
         +-MIRROR-+     +-MIRROR-+     |     +-STRIPE-+     +-STRIPE-+     
             |              |          |         |              |          
             +----STRIPE----+          |         +----MIRROR----+          
                     |                 !                 |



RAID 1+0 is far more commonly used, however, because it has better redundancy (smaller chance of array failure because of multiple drive failures). The probability of array failure for each RAID level is:




  • RAID 1+0: 1 drive fails: 0 (0%), 2 drives fail: ⅓ (33%), 3 drives fail: 1 (100%)

  • RAID 0+1: 1 drive fails: 0 (0%), 2 drives fail: ⅔ (66%), 3 drives fail: 1 (100%)


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