RAID for Rookies

RAIDing each level

RAIDing for Rookies

Before World of Warcraft fans get excited, this isn't about leading a group of Leeroy Jenkins's.  Instead, without further ado, we will cover the most fundamental levels of RAID schemes - RAID 0, RAID 1, RAID1+0, RAID 5 and RAID 6.

RAID 0, otherwise known as a Striping Array, is easily remembered as an all-or-nothing RAID, built purely for performance.  At its simplest definition, it splits up data into 'blocks' - these are distributed between the hard-disk drives in the array as equally as possible.  This allows larger data files to be processed faster as the individual hard-disk drives operated read/write in unison. Ultimately, this allows the combining of their respective blocks to form the complete data file far quicker than the file could be sought from a standard single hard-disk drive. 

On the flip-side, RAID 0 offers no redundancy.  This means that if one drive errors, loses integrity or fails, the entire RAID setup is virtually impossible to salvage - hence, the data stored on the RAID 0 setup will be forfeit.  Therefore, it could be possible to liken a RAID 0 setup to a fast single hard-disk drive; you have performance but no data parity.

RAID 1, is the antithesis of RAID 0.  It is typically consisting of two hard-disk drives which operate in unison, with the key difference being that they are exact sector-by-sector mirror of each other.  This offers no performance advantage, but in the event of a hard-disk drive failure, you can run off just the one remaining hard-disk drive.  They typically operate by a read request being fulfilled by one drive; yet write requests being fulfilled by both.  Wear-levelling has been known to be employed to share the read requests between drives to lengthen the lifespan of the RAID setup before failure.

RAID1+0 (or otherwise known as RAID10) combines the elements of RAID0 and RAID1.  That is, it consists of a striped RAID 0 setup which is made of a mirrored RAID (1).  This is sometimes deemed a suitable RAID setup for a compromise between speed and redundancy of data, however, in the event of a drive failure, the striped element of the RAID will not be able to operate at original speed – thereby taking a noticeable performance hit over the full array’ speed.  The mirrored element of this array allows a failed drive to be replaced and the array restored to original operational integrity, thereby allowing the array to be rebuilt with minimal difficulty.

Around-about this point, you may think that all possible beneficial setups for RAID have been established; you'd be incorrect however... 
RAID 5 is similar to RAID1+0 in that it has both striping (for performance) and redundancy, however, it differs in the method of its redundancy.  Instead of traditional mirroring of stripes, it will distribute the stripes across all bar-one of the hard-disk drives in the array - the final drive will be used to store the data parity - essentially a copy of the data in its entirety.  This might not sound too amazing if you are thinking that the data parity is retained on just one disk drive in the array, however, the RAID5 setup distributes the parity logically, and equally, across all drives, best displayed in the following diagram:


RAIDing for Rookies
RAID5 - simplified.  Maybe...  

 

As if RAID5 couldn't be improved upon further, an additional array, RAID6, was created. 

RAID6 caters for an additional parity (essentially a mirrored parity) being incorporated into the array.  This allowed for up to two hard-disk drives in the array to fail before the array would become 'at risk'; thereby offering the greatest array stability and recovery whilst still offering performance through striping.

  

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Most Recent Comments

06-02-2013, 09:41:18

tinytomlogan
New boy Matt joins the OC3D team and his first article is a Raid Guide. He says "It is time to dispel the mystique around the previously perceived 'hardcore' hard-drive setups..."

http://www.overclock3d.net/gfx/artic...172757757l.jpg


Continue Reading

06-02-2013, 10:26:37

Josh Weston
A great write-up.
Welcome to the team, Matt.

06-02-2013, 10:41:27

Spaceboy
Impressive write-up there

However, as an ex-storage consultant, please permit me to point out a few niggles

Page 2 - Raid 5 : You mention "Instead of the traditional mirroring of stripes"... I believe this should read "striping of mirrors" as you aptly described in the Raid 1+0 section above. Remember that striping of mirrors offers greater redundancy than mirroring of stripes (raid 1+0 is better than 0+1).

Page 2 - Raid 6 : The parity is not mirrored, it should be (in any decent implementation) a completely separate parity generation - this offers extra protection against bad blocks that store Raid-5 parity data during rebuild operations.

Page 3 - Mirroring : This attribute offers substantial performance gains for read operations, but none for write operations.

Page 3 - Raid FAQ 1 : Performance improvements are in-line with hard drives, eg: Raid-0 across 2 SSDs will double the throughput in both read and write operations. While real-life improvements may barely be noticeable, the performance increase is real. Also TRIM is now supported in Raid-1, so I argue that wear-rates are not substantially increased over a single SSD. I do agree it rarely makes financial sense though

Raid FAQ 3 : It is very possible to partition your different size drives and then use software RAID across like-size partitions. Leaving you with free partitions you can use for data storage, with the proviso they have no redundancy. Eg: 2TB + 500gb - partition the 2TB into 1.5TB + .5TB, then RAID across the 500gb partition and the 500gb drive. You can subsequently use the 1.5TB partition as normal.


I fully approve of the work you've put in to this and it is overall very good
I am however anally retentive having done this for a living for a while so I hope you'll take my comments as "constructive criticism" rather than any kind of dig

Keep up the good work!

06-02-2013, 17:35:08

f00f1ght0r
Thank you kindly folks for the welcome!

Spaceboy - i'm honestly impossible to offend, so don't worry about that. The article was aimed at beginners, so my intention was lay some basic phrases and general understanding in this article, and then 'polish it up' in future advanced articles.
I do bow to your knowledge on this subject though, I am but a Jack of All, Master of None, based on the comparison between our job roles!

06-02-2013, 19:26:55

Noz_God
Nice wright up

07-02-2013, 05:17:09

Diablo
Good work, I will agree with the RAID 5 comments - I tried a software/onboard method, and got a 5-6MBps throughput, when I upgraded to a dedicated RAID card (adaptec), that went up to over 200MBps.

07-02-2013, 08:23:40

ugiboy
Hi, very impressive & informative article, well done Matt, I look forward to the follow ups. If I have understood this correctly (which is doubtful) putting SSD's into Raid0 array has no performance benefits & speeds up degradation? I look forward to anyones opinions/thoughts. Cheers

07-02-2013, 09:36:00

tinytomlogan
Quote:
Originally Posted by ugiboy View Post
Hi, very impressive & informative article, well done Matt, I look forward to the follow ups. If I have understood this correctly (which is doubtful) putting SSD's into Raid0 array has no performance benefits & speeds up degradation? I look forward to anyones opinions/thoughts. Cheers

Yeah you have not got the grasp of it at all..... LOL

07-02-2013, 09:52:54

ugiboy
I thought as much lol

07-02-2013, 10:13:19

ugiboy
Beginner RAID FAQs
Q: Can I use Solid-state drives for a super-fast array?A: Yes and no... SATA3 and PCI-E SSDs are already ridiculously fast - RAIDing them will either present negligible performance improvement (for RAID0), or in the case of the mirroring and parity RAIDs, will greatly increase the wear rate of the SSDs, therefore reducing their lifespan. So it *is* possible, but it does not make financial sense in my honest opinion!


Tom, I have taken this from the FAQ section of the review. So can you explain what i have not grasped please. Cheers

07-02-2013, 10:41:50

tinytomlogan
Quote:
Originally Posted by ugiboy View Post
Beginner RAID FAQs
Q: Can I use Solid-state drives for a super-fast array?A: Yes and no... SATA3 and PCI-E SSDs are already ridiculously fast - RAIDing them will either present negligible performance improvement (for RAID0), or in the case of the mirroring and parity RAIDs, will greatly increase the wear rate of the SSDs, therefore reducing their lifespan. So it *is* possible, but it does not make financial sense in my honest opinion!


Tom, I have taken this from the FAQ section of the review. So can you explain what i have not grasped please. Cheers

You said about raid 0- that does make them a shit load faster even with onboard raid or software raid. The statement about degradation with other arrays is correct though but no different to intensive use.

Ive got 2x 480GB Corsair Force 3 GT's in Orca in Raid0 - read and write on the arrany is over 1GB/s

07-02-2013, 10:53:00

ugiboy
OK, thanks, I will run crystal disk to find out how my 2x120gb fair. I know my Ramdisk is about 8100mb read & write. Cheers

07-02-2013, 11:30:46

tinytomlogan
Just need to remember TRIM does not function with RAID so you need to make sure your SSD's have hardware level garbage collection or they will in no time at all run like dogs.

07-02-2013, 11:45:17

ugiboy
Thanks for that, will check it out. Cheers

07-02-2013, 15:18:50

Soda-88
RAID0 TRIM is supported by Intel's 6 and 7 series chipsets.
http://www.anandtech.com/show/6477/t...therboards-too

07-02-2013, 15:45:03

f00f1ght0r
Quote:
Originally Posted by Soda-88 View Post
RAID0 TRIM is supported by Intel's 6 and 7 series chipsets.
http://www.anandtech.com/show/6477/t...therboards-too
My personal thoughts are that in a 'beginners' article, we do not want to get into BIOS flashes, let alone Hex Editing live drives. This would, however, be ideal in the area at the bottom of the final page where I mentioned about going into things with greater depth

07-02-2013, 15:49:25

seumasbeathan
Great write-up mate I look forward yo reading more in the future

And welcome

07-02-2013, 16:13:10

ugiboy
My Asrock X79 extreme11 says it supports trim but i do not know how to enable or even check if it is running? any members have any idea to i could do this please.

07-02-2013, 19:15:35

f00f1ght0r
ugiboy - I haven't followed the research to the end of the internet looking into your system, but it appears to revolve around flashing the BIOS and, you guessed it, editing live file system hex.

It may support TRIM, but that is simply on separate SSDs, not on RAID perhaps?

On the official page for your mobo, it mentions RAID0, not RAID5 - speed is obtainable, but the lifespan and speed of the drive/s may be compromised without TRIM/hardware controlled garbage collection.

Microsoft advise that you can verify TRIM being active (not just able to be supported) through these steps:

Quote:
1. Start Menu > Run > "fsutil behavior query DisableDeleteNotify"
If the result is '0' TRIM is available (not necessarily active)

2. Install and run Intel's SSD Toolbox program (http://downloadcenter.intel.com/Deta...&DwnldID=18455)

3. Select your SSD and click "View Drive Information" (it doesn't matter whether it's an Intel SSD or some other brand)

4. In the "Word" column, scroll down to '169'; the description should be, "Data Set Management Support"

5. A couple of lines down from that, look for "Bit 0 - Data Set Management Supported"

6.If the Hex Value associated with that reads '1', the drive is ready to receive TRIM commands from the OS

That, along with the 'fsutil' command, should be sufficient to assume that TRIM is operating properly.

07-02-2013, 19:34:57

ugiboy
Hi, thank you for taking the time to reply and for the instructions. I have Intel's SSD Toolbox V3.1.2 and when i click the "View Drive Information" nothing happens? I will download it again to see if it works and hopefully follow your instructions. Thanks again Glen Hi, I have entered what you said in "command prompt" and it is telling me DisableDeleteNotify = 0. If i understand you correctly that means that "Trim" is enabled? Thanks Glen

08-02-2013, 14:14:51

f00f1ght0r
Quote:
Originally Posted by ugiboy View Post
Hi, thank you for taking the time to reply and for the instructions. I have Intel's SSD Toolbox V3.1.2 and when i click the "View Drive Information" nothing happens? I will download it again to see if it works and hopefully follow your instructions. Thanks again Glen Hi, I have entered what you said in "command prompt" and it is telling me DisableDeleteNotify = 0. If i understand you correctly that means that "Trim" is enabled? Thanks Glen
That does indeed mean that TRIM is supported in the OS yes

08-02-2013, 14:20:47

ugiboy
Thank you. Best Regards

14-02-2013, 17:21:54

MicroAlex
Thank you for the topic, filled a few gaps with things I did not know for sure
Reply
x

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