RAID guru needed

D

DougWD

Limp Gawd
Joined
Sep 4, 2005
Messages
502
I just ordered all of my parts and before they get here, I have a couple of RAID questions.

I got two Western Digital caviar black 640s. Now that I'm a little more up to date on RAID functionality, other than yeah you get a speed increase while transferring large files in RAID 0, I'd like to ask a couple more questions:

My MB only supports RAID 0,1, and 5. So those are my choices w/o buying a dedicated RAID controller.

Some of this may be incorrect, so please add in what is wrong.

RAID 0: Moron RAID. This was what I was initially going to use.
RAID 1: SMART RAID. Mirrored but with no performance over a single drive, and loss of 50% total capacity.
RAID 5: Better performance than Mirrored RAID 1, same level of redundancy (being one drive fail), but technologically complicated and minimum disks is 3. Loss of 1 disk capacity.

Questions:
1. If I load my system using RAID 0, and I cahnge the RAID configuration to RAID 1 or 5 later w/o reloading?
2. If I need to reload to change configurations, can I use Acronis Image to do that?
3. What is the performance trade off between RAID 0 and RAID 5?

If the RAID 5 performance hit is small, I may just get another Black 640 and use RAID 5. It's a good thing they are only 80 bucks right now.

Thanks a lot again for everyone's help.
 
Here's a brief overview on RAID and its levels:

tiraides said:
What the hell is RAID? What is it good for? Why is it good? What does it do?

RAID stands for Redundant Arrays of Inexpensive/Independent Disks (or some variant thereof), which integrates, via a RAID controller, two or more hard drives together for greater performance and/or data protection. There are many levels of RAID, with each level having its own strengths and weaknesses. Here are some explanations of RAID and its various levels. Please understand that RAID is NOT a backup solution.
Click to expand...

Though I'm no expert on RAID...

1. It's not really possible to change the RAID levels without "reloading" (reformatting?) due to the different way each RAID level handles data.

2. I'm not sure, but I doubt it. Remember that the way data is stored/handled in RAID 0 is different from RAID 1 and/or RAID 5. Acronis True Image is designed to create a cloned "image" of your hard drive setup.

3. See some of the links that I provided. For pure speed, RAID 0 is the fastest of the RAID levels.

... Of course, I could be wrong....
 
Might want to ask a mod to move this thread (don't make a new one) over to the Data Storage subforum we have. Your questions are more suited/specialized/specific for their area of expertise.

But to clear up a few things:
- RAID5 is actually slower than the RAID1 since three different sets of parity data is written across at least three drives. Granted this link is from three years ago, it should still be accurate to this day:
http://blogs.sun.com/mrbenchmark/date/20050420#raid_1_vs_raid_56

- On integrated software RAID controllers (like those found in every consumer motherboard professing RAID support), RAID0 is significantly faster than the RAID5. About three times as fast IIRC. Since the PC's CPU is being used to do all of the parity calculations with a RAID5 setup (on integrated RAID controllers), you do incur serious performance hits with RAID5.

It's only with true hardware controllers where there's a separate XOR CPU doing all of the parity calculations that RAID5 actually outperforms RAID 0 on integrated RAID. How much a hardware controller based RAID 5 setup outperforms a RAID 0 setup on intergrated RAID depends on the controller itself, what drives are being used, what interfaces, etc.

- AFAIK, you cannot move between RAID 0, RAID 1 or RAID 5. I think you can turn a RAID 5 array into a RAID 6 array.

But another warning: Not exactly a RAID Guru myself.
 
I have a good bit of experience with raid and Danny Bui is right.

Except you can move from one form of array to another BUT it is accomplished by imaging your raid setup to another drive. And then changing your raid array (this will erase the data on the array) and re imaging the data back to the changed array. IF Acronis True Image works like Ghost (I don't have any experience with Acronis) than it will work fine for this task. The raid setup information is handled by the raid controller and raid driver not by the hard drives so as long as the raid driver is installed to the OS you can image any drive/array to any other drive/array.
 
Danny Bui said:
- AFAIK, you cannot move between RAID 0, RAID 1 or RAID 5. I think you can turn a RAID 5 array into a RAID 6 array.
Click to expand...
Decent RAID cards will allow you to go from RAID 1 to RAID 5. You can convert a RAID 5 array into RAID 6 as well.

I personally don't recommend any RAID level with parity without a hardware RAID controller.
 
dr.sandman said:
Except you can move from one form of array to another BUT it is accomplished by imaging your raid setup to another drive. And then changing your raid array (this will erase the data on the array) and re imaging the data back to the changed array. IF Acronis True Image works like Ghost (I don't have any experience with Acronis) than it will work fine for this task. The raid setup information is handled by the raid controller and raid driver not by the hard drives so as long as the raid driver is installed to the OS you can image any drive/array to any other drive/array.
Click to expand...

Blue Fox said:
Decent RAID cards will allow you to go from RAID 1 to RAID 5. You can convert a RAID 5 array into RAID 6 as well.

I personally don't recommend any RAID level with parity without a hardware RAID controller.
Click to expand...

Thanks for the clear up guys.
 
Also of note is that raid 1 does increase performance over a single drive.. read operations perform about double due to have two disks to read the data from.
 
RAID 0 is for performance.
RAID 1 is for uptime,
every other RAID is a compromise between the two, with varying levels of protection and performance.

RAID IS NOT INTENDED FOR THE PROTECTION OF DATA, nor should it be used for that. You are still required to keep your important data backed up. No level of redunancy will protect you from corrupted installs, bad drivers, viruses, catastrophic losses, and user error.
 
serbiaNem said:
Also of note is that raid 1 does increase performance over a single drive.. read operations perform about double due to have two disks to read the data from.
Click to expand...

I've heard that... and intuitively it ought to work that way, but have never seen it and have never seen a benchmark proving it, so I'm skeptical.

With the low price of HD space these days, I think more folks who consider a parity solution ought to give more thought to a RAID10 setup. It doesn't take a card costing many hundreds of $, and you get both improved data transfer as well as HD failure protection.

But to chime in on Ryan's post above.... if you aren't backing up now and are considering a RAID configuration, then reconsider your priorities.
 
Blue Fox said:
Decent RAID cards will allow you to go from RAID 1 to RAID 5. You can convert a RAID 5 array into RAID 6 as well.
Click to expand...

You can do these things, but in my experience it takes ages and often goes very, very wrong, absolutely essential to have a backup/image before starting.

At which point you may as well just nuke the array and start over, saves a lot of time. (obviously, this only really applies for stuff you can afford the downtime on)
 
serbiaNem said:
Also of note is that raid 1 does increase performance over a single drive.. read operations perform about double due to have two disks to read the data from.
Click to expand...

Theoretically, but in actuality false. This comes up again and again, but if you look at benchmarks, there is no RAID hardware manufacturer who has bothered to implement this.

RAID 1 is generally in actual use, slower than a single drive. (slightly)
 
Very interesting stuff.

If I were to go with RAID 0 + 1 for a three drive set up, one drive as a mirror, I'd have to get a controller card, since my MB only supports 0,1,and 5. And 5 takes too much CPU power using the on board RAID controller.

It does make sense that if you image a drive that is raided, it should work on any other drive--given you are imaging back to teh same system. I've actually imaged from one drive, and then re imaged another drive completely different from the original, like from a WE 3.5 RE2 to a Samsung 2.5, and everything worked fine. In fact, I used the 2.5 connected externally with a USB cord to boot from. No problems.

One thing about True Image 10 and now even 2009: It won't boot with its boot disk on many SATA DVD/CD ROMS becuae of some Intel SATA controiller. Lots of people are geting teh "Fatal error cannot find bootdisk" error when trying to boot with the TI 11 and 2009 created bootdisk. I jsut got that error tonight on a new HP laptop with Intel chipset and SATA DVD drive. If you are using a IDE DVD then you are ok.
 
Blue Fox said:
RAID 0+1 requires 4 drives minimum.
Click to expand...

True- AND raid 0+1 (usually called raid 10) needs to have an even number of drives. And with all raid setups it is highly(cant stress it enough) HIGHLY recommended or most of the time required to use disks that are the exact same size and model number. I have setup one or two raid 1 arrays with different size of disks but always recommend against this.

And I always recommend not using your motherboards raid controller it is safer to use an add on card even if it's a cheap software add on card. If your have your array for a while on your motherboard and the board dies you might get screwed. If you can't find another board that matches yours with the same raid controller you will not be able to recover your array. And you can always move an array to a different system without data loss using an add on card.
 
I've actually imaged from one drive, and then re imaged another drive completely different from the original, like from a WE 3.5 RE2 to a Samsung 2.5, and everything worked fine.
Click to expand...

With that analogy, nothing was actually changed, just transferred.

Changing RAID modes would be more like going from NTFS to FAT 16......lots of stuff can happen and it's not all good.

Then you have the differences between software and hardware RAID.........
 
OH yea - I don't really recommend using ubber cheap raid cards either. You can get a Promise or Adaptech card for a reasonable price if you need something cheap. I have had good luck with both these brands.

If True Image is worth a shit than it will give you the option to create a bootable system disk/cd that has your controller drivers built in to it so that you can use the program. This will allow you to get around the problem you were having with the SATA drive.
 
Old Hippie said:
With that analogy, nothing was actually changed, just transferred.

Changing RAID modes would be more like going from NTFS to FAT 16......lots of stuff can happen and it's not all good.
Click to expand...

Old Hippie might have been trying to make a different point and used a horrible analogy. Changing raid modes is completely safe if done properly. Use the imaging method. Nothing with your data gets changed as far as your operating system or any software is concerned. The os/software talks to the driver just like it would with a non-array. The driver is the buffer between the array and the software/os and works the same way it does on a single drive.
 
Old Hippie might have been trying to make a different point and used a horrible analogy
Click to expand...

I guess I'm just confused, as usual! :D

I'm sure there's a major difference between converting an array just using the controller and imaging an array to convert to a different mode.

How's that? ;)
 
http://www.freepatentsonline.com/7334156.html

The link has a good explanation on raid controller conversion. I guess after doing it many times I just like the imaging option more than the controller based conversion(it can also be a lot faster). However imaging is not always an option and you have to use the controller based option. You have more of an option with a home pc to use imaging than you do with a server due to the size of the drives typically in use. I know I can't find a single drive to image my backup system array to - its way to big. Also adding more drives to an array uses the same principal as doing a controller based conversion and people do that all the time.

Edit. I forgot to add the standard backup your shit disclaimer when working with your data - no matter what you are doing.
 
dr.sandman said:
True- AND raid 0+1 (usually called raid 10) needs to have an even number of drives.
Click to expand...
RAID 0+1 and RAID 10 are not the same; very similar, but not identical. The order in which things are done are swapped (one is a mirror of stripes, the other is a stripe of mirrors).
 
Blue Fox said:
RAID 0+1 and RAID 10 are not the same; very similar, but not identical. The order in which things are done are swapped (one is a mirror of stripes, the other is a stripe of mirrors).
Click to expand...

100% correct - I usually hate splitting hares and just added a quick quote that it is usually call it raid ten

this is a copy and paste from wikipediia~
"As there is no basic RAID level numbered larger than 9, nested RAIDs are usually unambiguously described by concatenating the numbers indicating the RAID levels, sometimes with a "+" in between. For example, RAID 10 (or RAID 1+0) consists of several level 1 arrays of physical drives, each of which is one of the "drives" of a level 0 array striped over the level 1 arrays. It is not called RAID 01, to avoid confusion with RAID 1, or indeed, RAID 01. When the top array is a RAID 0 (such as in RAID 10 and RAID 50) most vendors omit the "+","
 
dr.sandman said:
OH yea - I don't really recommend using ubber cheap raid cards either. You can get a Promise or Adaptech card for a reasonable price if you need something cheap. I have had good luck with both these brands.

If True Image is worth a shit than it will give you the option to create a bootable system disk/cd that has your controller drivers built in to it so that you can use the program. This will allow you to get around the problem you were having with the SATA drive.
Click to expand...

I created it with my current system, and then tried using it on a newer system. I've used it on all sorts of other systems to image drives from the boot disk. I'll try loading it on the new system and then creating a bootdisk that way.
\
After reading all of yuor posts, I think I may get a RAID controller card and one more 640 black. What RAID will allow me to run two 640 blacks in striped mode with the third 640 black as parity Or, whatever you call it when you can run two striped and one acts as a safety disk. or mirror?) Is this thre disk mirror/safety disk parity LOL a god thing to run for speed and redundancy, or is it not so good? You could just tell me also what RAID configurations will allow both speed and redundancy. I don't think I would go RAID 1. I'd just back up my disks everyday, like I do now. The main thing is that I want to try the RAID 0 speed and see if it really makes a difference to me. However, like you have all stated, RAID 0 is like lighting a rocket off under your ass with no parachute. That makes me a little uncomforatable.

Another good point that someone made was that with on board controllers, if you lose the MB you lost the array, unless you can get the exact MB again. With a controller card, you can swap out the card and retain the array. Again, I'm not too keep on a one system drive, since you may have to swap the array to get back information booted from another computer.

I have looked on Gigabyte's website and they say my MB will do RAID 0,1,5 and 10. Is RAID 10 the same processor hit as 5?

All of the sudden RAID is sounding a lot less "fun." Where's my old SCSI drive.
 
The raid mode where two drives (or more) are striped and the last one is used for parity is raid 5. As mentioned before raid 5 with out a hardware based controller card will cause your system a performance hit. Raid 10 doesn't experience the same performance hit because it doesn't use a parity drive. You can not mirror a striped array to one drive!!! you HAVE TO mirror the striped array to another matching striped array (or you can stripe multiple mirrored arrays-makes no difference really). This means you have to have at least 4 drives in order to used raid 10. I think a lot of people get confused as to what we mean when we say "hardware based raid controller card" - a hardware based controller card has a processor built in to it to calculate the info needed to use parity. Not every add on card has this processor - in fact most do not and you typically spend about $200ish on a decent card that does support the on-card processor for parity.

With raid 5 you get all of the drives used minus 1 for capacity and with raid 10 you get half the capacity of all the drives used. SOOO - 3 drives minimum required with raid 5 using the WD640s will give you 1280 for capacity. But the 4 drives minimum required for raid 10 using the same WD640s will still give you 1280 for capacity even though you have 4 drives instead of 3.

Cost break down.
Raid 5 - 3 drives at $75 plus raid card @ $200ish would equal $425ish
Raid 10 - 4 drives at $75 and you can use the option of an add on card @ about $70ish would equal $300-$370
 
DougWD said:
I created it with my current system, and then tried using it on a newer system. I've used it on all sorts of other systems to image drives from the boot disk. I'll try loading it on the new system and then creating a bootdisk that way.
Click to expand...

I haven't used True Image but I don't think this approach will work. RTFM

Edit. Oh yea - don't be afraid of RAID - once you get it figured out and choose what you want it should be a set once and forget experience. If you do a little reading and don't set your expectations to high RAID is kick ass. GOOD LUCK
 
dr.sandman said:
The raid mode where two drives (or more) are striped and the last one is used for parity is raid 5. <snip>
Click to expand...

RAID five doesn't stripe between two drives and use the last one for parity. All drives are used the same equally rotating which one is used to store parity data..

Code: 
[U]Disk 1  |  Disk 2  | Disk 3[/U]
Data A1 |  Data A2 | [COLOR="MediumTurquoise"]Parity[/COLOR]
Data B1 |  [COLOR="MediumTurquoise"]Parity  [/COLOR]| Data B2
[COLOR="MediumTurquoise"]Parity  [/COLOR]|  Data C1 | Data C2
Data D1 |  Data D2 | [COLOR="MediumTurquoise"]Parity[/COLOR]
Data E1 |  [COLOR="MediumTurquoise"]Parity  [/COLOR]| Data E2
[COLOR="MediumTurquoise"]Parity  [/COLOR]|  Data F1 | Data F2

... and so on


EDIT: And just for kicks, a four drive example


Code: 
[U]Disk 1  |  Disk 2  | Disk 3  | Disk 4[/U]
Data A1 |  Data A2 | Data A3 | [COLOR="MediumTurquoise"]Parity[/COLOR]
Data B1 |  Data B2 | [COLOR="MediumTurquoise"]Parity  [/COLOR]| Data B3
Data C1 |  [COLOR="MediumTurquoise"]Parity  [/COLOR]| Data C2 | Data C3
[COLOR="MediumTurquoise"]Parity[/COLOR]  |  Data D1 | Data D2 | Data D3
Data E1 |  Data E2 | Data E3 | [COLOR="MediumTurquoise"]Parity[/COLOR]
Data F1 |  Data F2 | [COLOR="MediumTurquoise"]Parity  [/COLOR]| Data F3
Data G1 |  [COLOR="MediumTurquoise"]Parity  [/COLOR]| Data G2 | Data G3
[COLOR="MediumTurquoise"]Parity[/COLOR]  |  Data H1 | Data H2 | Data H3

... and so on.
 
ryan_975 said:
RAID five doesn't stripe between two drives and use the last one for parity. All drives are used the same equally rotating which one is used to store parity data..
Click to expand...

Yes I'm sorry - brain fart - ryan is right - raid 5 uses distributed parity
 
RAID 3 and 4 use a dedicated parity drive, but they are rarely used (RAID 4 especially).
 
ADG

damn SCSI is ahead in that part with dedicated RAID controller PLUS copious amount of cache (128MB minimum with up to 6GB). At least the HP, Dell RAID controllers!
 
figgie said:
ADG

damn SCSI is ahead in that part with dedicated RAID controller PLUS copious amount of cache (128MB minimum with up to 6GB). At least the HP, Dell RAID controllers!
Click to expand...
You can get SCSI controllers with no hardware RAID and no RAM. Likewise you can get SATA/SAS controllers with hardware RAID and RAM (and even IDE if you look on eBay). There is no point in buying anything SCSI at this point since they have pretty much been replaced with SAS.
 
serbiaNem said:
Also of note is that raid 1 does increase performance over a single drive.. read operations perform about double due to have two disks to read the data from.
Click to expand...

only with decent controllers this happens, my ICH9R raid 1 performs the same as a single drive.
 
Blue Fox said:
There is no point in buying anything SCSI at this point since they have pretty much been replaced with SAS.
Click to expand...

Blue Fox,

what does SAS stand for?

Serially Attached SCSI

It is STILL scsi, just the interface has changed, perfromance improvements etc no different than when the went from SCSI to U320. Still SCSI. Just a different plug along with the gains there. ;)
 
figgie said:
Blue Fox,

what does SAS stand for?

Serially Attached SCSI

It is STILL scsi, just the interface has changed, perfromance improvements etc no different than when the went from SCSI to U320. Still SCSI. Just a different plug along with the gains there. ;)
Click to expand...
No one calls SAS SCSI. Sure, it is part of the name, but when someone says SCSI, they mean old U160/U320 drives. Just like no one calls SATA drives ATA because most people identify that with IDE drives.
 
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