RAID for Rookies

Round-up and Recap

RAIDing for Rookies

Summary of Terms

In this brief written introduction to RAID setups, you should now have an awareness of several variations of RAID (unless you did already!), and more specifically their general areas of expertise.  To summarise several key terms:

Performance; this is gained by striping data across multiple drives - thereby allowing data to be processed in synchrony without delays in read/write/seek times.  This attribute offers no safety-net, so if an error occurs on ANY hard-disk drive, it may likely damage the entire array.

Mirroring; this copies data across multiple drives - should one drive, or data element be corrupted or damaged, it will allow the same data to be read from another drive in lieu of the original.   This attribute offers no performance gains.

Parity; this is allows for each data file to have a structured, complete copy placed within the array - should a drive fail, each data file will be able to be fully recovered from either the data parity, or the data stripes.

Homogenous; in RAID-terms, is defined as consisting of near-identical hard-disk drives.  Fully identical drives are difficult to achieve based on variation in disk structure, spin-speed and other physical characteristics; however, same brand, same quoted storage media size and same model are typically sufficient to fit our definition of homogeneous.

Heterogeneous; specific to RAID, this simply means 'non-identical'.  This could be as simple as different manufacturers, different models, or even, in some setups (not recommended, and difficult to construct a RAID with) different capacity hard-disk drives.

 

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 software RAID0, based on the lack of TRIM support in RAID; 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!

Edit: A brief side note SSD in a RAID0 setup, supporting hardware-level garbage collection will avoid negative issues surrounding performance degradation - but once again, speed and cost are two factors that most of us must balance carefully!

 

Q:  Software RAID or Hardware RAID - which is best?

A:  Neither outweighs the other in a direct comparison, however, they both have their contrasting strengths and weaknesses.  Software RAIDs excel at being forensically easier to recover (in the event of an error), whilst hardware RAIDs can be notoriously troublesome to restore.   Cost is important, and this is where software RAID, once again beats hardware RAID, in being a far cheaper setup.  
Software RAIDs are ideal for high performance enthusiast workstations or home servers, whilst hardware RAIDs offer features (such as hot-swapping and performance increases) which are far more beneficial to enterprise level server farms and clusters.
On the subject of performance increases, the larger array setups of RAID5 and RAID6 - consisting of 4 or more hard-disk drives - require some hefty processing overheads which can substantially dominate I/O data in a software/onboard RAID controlled system.  The benefits of a separate hardware RAID controller are that it frees up the core system processing for other tasks and maintains the RAID without involvement from any other hardware or software.  This often explains end-user complaints of RAID5/6 setups being particularly underwhelming, and sadly, always ends up costing more money at the end of the day as they are forced to abandon their RAID5/6 setup, or walk the path of the hardware RAID.

 

Q: So, I have 2 hard-disk drives, a 2TB and a 500GB - can I RAID them?

A: This depends entirely on the controller.  Some will allow different drives (i.e. heterogeneous) to be used together, however they will place a limiter on the larger drive.  This basically reduces the larger drive to only use the capacity of the smaller drive.  So in short, you are wasting 1.5TB of capacity, for the benefit of a RAID setup.   Not the best use of space...

Q: Is it true RAID can only run with SATA connected drives?

A: Absolutely not - you can have IDE, SATA, Serial and SAS drives deployed in RAID setups without issue.  The only issues will be bandwidth, noise and heat.  For instance, SAS are renowned for being high-speed drives (15k spin speed typically), which generates a lot of heat and noise; additionally, peak power (during start-up) can sometimes cause issues on older system PSUs unable to supply the required voltages.

Coming soon - RAID expanded; how to deploy your own RAID setups; more jargon and an unhealthy amount of fundamental hard-disk drive inner-workings to satiate the inner-techie in all of us!

 

Author's Note

This article is intended as an appetite-whetting device for enthusiasts who are new to RAID, or those who simply want to refresh their knowledge.  Myself and colleagues at OC3D all know that RAID setups can become a whole-lot more complex than this article, so hang-fire, and we will boggle you in future articles! Discuss your thoughts in the OC3D Forums.  

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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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