RAID FAQ V1.3.1 - Page 2
Forum Storage : Hard Disks - RAID FAQ V1.3.1
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| LabaR wrote : I'm still confussed on the difference between Raid 0+1 and Raid 1+0. Raid 0+1 seems to make sence...Raid 1+0 does not. |
A lot of people become confused by this because they usually only think of a RAID array as containing a small number of drives. For example, RAID0 or RAID1 arrays are usually built using two drives, no more. However, consider a system using 8 drives for a RAID array. We are after redundancy here, because it's a RAID array after all, and RAID5 is too slow for what we want to do, plus drives are cheap these days, 8 drives, no problem. So we're going to make a RAID array that consists of mirroring and striping. Our newbie tech guys things, RAID0+1, no problem, solves all our worries.
In this configuration of drives we have the following
M I R R O R
Array1 => Array2 = Drive
RAID 0 + RAID0 = RAID0+1
S
T 1 5
R 2 6
I 3 7
P 4 8
E
Two separate striped arrays of 4 drives each, mirrored, RAID0+1. Okay, consider, our techie is feeling pretty smug about his data all nice and safe except 6pm Firday evening, drive 3 decides to go down. Now what do we have?
DOWN + RAID0 = RAID0
1 5
2 6
(3) 7
4 8
A non-functional RAID0 array and it's mirror, RAID0 array 2. So now all our mission critical data is stored on a RAID0 array!!! That's BAAAD, suddenly what our techie thought was a nice secure RAID0+1 array has become a super scary RAID0 array. Unfortunately for our techie the RAID0+1 arrray is situated offsite and he can't get to it until Monday morning. In the meantime, disaster strikes and drive 5 in array 2 decides to go down. End of array!! Data lots, customers pissed etc.
So why does our techie wish he'd made a RAID10 array? Take a look, same situation, drive 3 and 5 have done down, but look the array is still functioning perfectly.
MIRROR S
Array1 RAID1 1 => (5) T
Array2 RAID1 2 => 6 R = DRIVE
Array3 RAID1 (3) => 7 I
Array4 RAID1 4 => 8 P
E
Although there's no difference between RAID0+1 and RAID10 with regard to the data on the drives, that is, in the RAID0+1 array the data on drives 1 and 5 is exactly the same as the data in the RAID10 array, the essential difference is the way in which the controller access the data. Because a RAID0+1 array consists of two RAID0 sub-arrays the controller only sees the two separate sub-arrays, it isn't set up to read between them (then it would be RAID10), hence it only requires one drive in each of those sub-arrays to go down to cause the whole array to fail. In a RAID10 array you need two drives in the same mirror sub-array to go down. If you do the math you'll realize that, particularly as array size increases, the chances of a RAID0+1 array failing increase with the more drives you add, whereas the chances of a RAID10 array actually decrease (given that there is no measure for the chance of a particular drive failing, drive failures are reported in MTBF for groups of drives).
Hope that makes sense.
In addition to the point made above, that RAID 10 can handle more failure modes than RAID 0+1 can, there is another important difference: When a bad drive is replaced in a RAID 10, there are only 2 drives involved in the rebuild - the working drive of the mirror and the new drive. With a RAID 0+1, once a drive is replaced, all 8 drives in the array are involved in the rebuild. This increases the chance that the array may suffer another failure before the rebuild completes, which will lose all data.
RAID 10 is generally always the best choice for a RAID 0/RAID 1 nested combination. One problem that you run into is that many motherboard-based and software/firmware-based RAID solutions implement only RAID 0+1 as their nested level. Some even go so far as to claim they do RAID 10, when they're really doing RAID 0+1.
"Did he dazzle you with his extensive knowledge of mineral water? Or was it his in-depth analysis of, uh, uh, Marky Mark that finally reeled you in?" - Troy Dyer (Ethan Hawke), Reality Bites, 1994
Reply to SomeJoe7777
Query: I am trying to set up RAID0 on XP Pro64 (already installed). Although I can not see the second SATA in "My Computer", I have, nevertheless, gone into disk management and converted both to "dynamic". My problem is that, when I go in to add a new volume/striped, the new volume wizard will only allow me to select "simple"... Striped and Spanned are grey'd out. Any thoughts?
What software can be used to create a USB RAID 1 mirroring hard drive for a laptop? Unlike a desktop, laptops often don't have the hardware capability for two HD RAID 1.
I have two disk used to set as Raid 0, and another disk as ACHI . I accidentally set them as Raid 5, and created a 50G partition. After that, I realized that my third disk became a member of Raid 5. Is there any way I can undo and get my data back from my third disk?
Gigabyte P35-D3R
Intel Sata controller
thanks
lol i have a feeling thats copied and pasted from the wiki article...
Great guide, but I have one question.
If Windows (Vista, in my case) is already installed, can one then set up a RAID without reinstalling the OS? It seems that you wouldn't be able to because it would have to stripe all of the data. Clean installs of Vista are always good but less so if you cheaped out and got the OEM.
Reply to Eggrenade
I have a question:
I have a 250gb WD right now, I am buying 3 more 250gb's to set up RAID 0+1.
I have backed up everything with Acronis TrueImage 11. Can I just back it up with that because it saves the entire drive, or do I have to reinstall Vista because of the RAID
no because in the bios when you put the four drives to raid0 the windows installer sees it as one 1tb drive.
so it will be 
the same and will just think it is on one big drive
for a home pc is it worth doing a mirror raid set up, as i am just looking to back up all data as you can re install the applications again if worst comes to worst or do a ghost if advisable. Would i just be best to do a back up once in a while of the data stuff and copy data files on my external drive. Also doesnt the mirror raid slow things down a bit.
can anyone advise if this only slows things down when you are copying something or will this be slowing things down in general in the background.
thanks
Hi there, and apologies in advance for the lengthy post this has turned in to.
I've been scouring the Internet for a day and a half now trying to find an answer to my issue, but to no avail.
I'm trying to set up my first RAID array. I have an ASUS 64 Bit AMD system with an M2N -MX SE mobo with NVIDIA GeForce 6100/nForce 430. I'm trying to install Vista X64 Ultimate .
I have encountered so many different suggestions and such that I thought it best just to ask outright what would be the best solution for me.
I have two Seagate Barracuda 250GB HDDs connected by SATA. My mobo only has two SATA connectors, so I've reluctantly removed the SATA optical drive and connected my old IDE one. I also have an old Maxtor 80GB IDE drive that I was considering using as the OS/Apps drive, leaving the others purely for the video footage I'll be editing (hence the RAID array).
So, my first question is, would this be a viable option? I'm sure that three drives would be better than two so I can keep the OS seperate from everything else, but would an older drive (I'm not able to afford another new one for the foreseeable future) just complicate things even further? Also, could this HDD be connected via the same IDE cable as the optical drive, or would I need another cable and if so, what would this mean for the jumpers on the back of each drive?
Secondly, I've been trying to install just to the two-disk array. I have set up the array using nVidia MediaShield so that its bootable, however, am hitting the (popular, it seems) problem of not having RAID drivers installed and Vista not seeing my RAID array for installation. I've downloaded the latest nVidia drivers for my board and o/s and have them on a USB stick at the moment. Can I install these from the USB stick during installation, or do I need to streamline them to a Vista disc using vLite, which is another suggestion I've come across? I'm new to these matters, as you can no doubt tell, but any help would be massively appreciated, as I'm just going round in circles at the moment.
Thanks...
I red an thread asking about it...
anyway, I always go for RAID 5 because of its simple, economical and easy configuration.
I have a WD 300gb velociraptor and a WD 640 7200rmp, If I do RAID 0 I will get better performance and would show only one drive as like 900GB? Also I am guessing I will have to install vista 64bit again for a fresh install?
RedDread -
You said you have the latest drivers, which is awesome, but have you checked the BIOS version. I would download and flash your BIOS if it is not. Usually I wouldn't recommend this but since you appear to be having issues it could help out. Your latest BIOS version is M2N-MX SE BIOS 0501. Also, you said you have set up your RAID array in the Nvidia Mediashield, but you also need to tell your BIOS how to recognize your SATA devices. Have you configured your SATA ports in the BIOS to be recognized as RAID or BASE (or something along those lines). In my experience, Vista has done an excellent job of detecting and installing on RAID volumes without 3rd party drivers. My guess would be that a BIOS setting is to blame for the non-detection and not the drivers. Does this board use the good old Pheonix Award Bios, and if so, what version?
I have worked with a couple different versions of the Nvidia RAID manager and have always had a good experience.
As far as your IDE drive goes, you can indeed install it on the same IDE header as your optical drive, and my recommendation would be to set both the optical drive and HD jumpers to CS (cable select). I would still recommend persuing the RAID boot partition, as I have done this on my last few PC's (currently have two velociraptors in RAID 0 w/ Vista Ult x64), and the performance boost is significant.
Oh yeah, and as far as keeping your OS seperate, it is a good idea to do so. If it were my setup and I only had the two drives, I would set them up in RAID 0, and at install (you'll get there!), I would partition off 60-80GB for the OS, and partition the rest for your media. This way, if you have an OS file corruption or the PC crashes, you can reinstall on your OS partition without affecting (deleting) your media!
Good Entry! Raid Array/Server Terminology is also very useful!
Message edited by salvationdata on 02-13-2009 at 07:42:04 AM
I feel it should be mentioned that most of the time when working with a small number of drives, RAID is not essential. Most of my builds rely on a minimum of 3 drives before I start going with RAID. 1 for the OS and typical system utilities like AV/Firewall and small programs. 2nd Drive for Large Programs like Office, CAD, and Games. And a 3rd Drive for Storage, including My Docs. Create a swap file on at least the first 2 drives. The Storage drive is usually a slower model to increase capacity, so I typically don't swap to that. This 3 drive set-up will typically produce more real world responsiveness then putting all your eggs in one basket. When I RAID, my first priority is redundancy on the storage drive using 1, 1E, 10, or 5. I've never seen RAID 5 be real useful in performance terms until you have at least 4 or 5 drives, especially with the new 1E level for 3 Drives. After this, now I finally consider RAID 0 for the OS and Program Drives. As you can see the number of drives can increase quite a bit here. Of course, with the emergence of SSD's with there unbelievable random access times, combining the OS and Program Drive to 1 Drive is finally an option.
I've taken this concept very far with 3x 15K scsi RAID 0 for the OS, 6x 10K scsi RAID 0 for Program Drive, 6 x 10K scsi for a scratch/download drive, and a 14x 10K scsi drive RAID 50 for storage. I also had 2 Hot Spares. Of course, everyone is not as nuts as me, and it took my own reactor to power it all...LOL
It should also be mentioned that it is typically better to create any partitions at the controller card level, rather than in windows. This gives you the ability to adjust stripe size and such for each partition. Most HBA manufacurers recommend this over windows partitioning. Some cards even let you create "sliced" partitions that let you choose different RAID levels on different portions of the same array. Just be careful when choosing swap file locations, as windows will see these as individual drives, thus negating the performance gain of spreading out your swap files if they're on the same array.
In conclusion, I would take 2 single non-raided drives and 1x RAID 1 for storage any day over a single large 4x RAID 0 array. Just my 2 cents.....
A couple more things to add...
I would never ever ever use a RAID 5 as an OS/boot drive ( it was recommended in an earlier post for its supposed simplicity ). The parity overhead is far to high for the small random reads and writes that an OS performs ( even with new cards ). This goes for swap file drives too. All HBA manufacures recommend against this AFAIK.
There have also been numerous studies on the inherent flaws in any "parity using" RAID level also. If 1 drive in an array develops a write error, but still continues to function, the error is replicated in parity across the entire array on the next read/write cycle before you know it has happened. Most hardrives don't just die, they show warning signs along the way. Using mirroring, this same situation would not be an issue. If 1 drive has a write error, the mirrored drive still holds the correct data. On the next read/write cycle the controller would know there is a discrepency between the data making recovery possible. In todays era of dirt cheap, large capacity drives, parity RAID should be avoided unless absolutely needed.
On a side note, yes you can create multiple hardware RAID levels on the same array of disks, using "sliced" partitions as mentioned above on some controller cards. I used to do it all the time on my old MegaRAID 1600 Enterprise. The only problem is combining RAID 0 on 1 slice and RAID 5 on another. If the RAID 0 slice would fail for any reason, the RAID 5 slice would be lost. RAID 0 and RAID 10 slices on the same set of drives worked like a charm though. It was useful to keep my almost never accesed set-up files safe, while using RAID 0 on the fastest part of the drives for the OS before I had a plethora of drives to play with. I might even do it again on my new build if my current controller supports it.
Finally, for those that are really ready to fry their brain, look into "positioning" benefits on different RAID levels. In the real world, its just as important as throughput.
Hi, I've just bought a 2nd 320gb drive to set up a RAID 0 array. I currently have OS and all programs on a 140gb drive and my 320gb drive is full of video files. Will combining the new drive with the existing drive mean I lose all my video files or will they just get striped across the new RAID array? If the drive gets formatted I guess I'll just not bother with RAID since I cba backing up 320gb of video onto DVDs... Thanks.
| youngtrotsky wrote : Hi, I've just bought a 2nd 320gb drive to set up a RAID 0 array. I currently have OS and all programs on a 140gb drive and my 320gb drive is full of video files. Will combining the new drive with the existing drive mean I lose all my video files or will they just get striped across the new RAID array? If the drive gets formatted I guess I'll just not bother with RAID since I cba backing up 320gb of video onto DVDs... Thanks. |
When you stripe it, it reformats both drives, you need to back up what you have now to a seperate disk, then once you RAID0 your two 320s you can move everything back.
Hi friends.. i am new to this forum and i would like to know about the concept called "hot swapping".. could any one please brief me about it?
Hot swapping means you can connect and disconnect hardware without powering down your CPU, like you should with other cables/interfaces that do not support this.
Hot swappable interfaces are USB and Serial ATA. Hot swap support is only mandatory for SATA 3Gbps controllers, though some other 1,5Gbps controllers also support them.
In order to use this feature on Windows, you need to have AHCI enabled in your BIOS (not "SATA" or "IDE" mode) and you'll see a green arrow in your system tray which when clicked prompts you with several removable devices. Your DVD-player and harddisks should also be in this list. Though you cannot remove your system disk, you can remove other harddrives not in use.
This feature is especially important for businesses since they do not want to power down their machines for a simple harddrive swap. For consumers this is of lesser concern. Enabling AHCI mode will also enable the use of NCQ (Native Command Queueing) a feature that SATA borrowed from SCSI-interfaces. NCQ can improve performance in some cases, but generally provides few or even negative benefit to home users.
ga-ma790fx-dss f2
phenomen
new WD caviar 4 hdd in raid 10 configuration
raid bios 2.5.1540.36
on load it gives me
id#1
2x2 raid 10
640136mb
track mapping
65535/255/63
functional
i got myself 4 hard drives for raid system
set it up,
went into bios
it is single "harddrive" in boot priority menu as scsi-0 raid ary1
set up my cdrom to be first device to boot from
and now when i tried to install windows it gave me
upon trying to boot from cd
DISK BOOT FAILTURE, INSERT SYSTEM DISK AND PRESS ENTER
I AM IN THE DEAD END, and dont know what to do, if anybody familiar, please walk me through.
RAID is an acronym first defined by David A. Patterson, Garth A. Gibson and Randy Katz at the University of California, Berkeley in 1987 to describe a Redundant Array of Inexpensive Disks,[1] a technology that allowed computer users to achieve high levels of storage reliability from low-cost and less reliable PC-class disk-drive components, via the technique of arranging the devices into arrays for redundancy.
More recently, marketers representing industry RAID manufacturers reinvented the term to describe a Redundant Array of Independent Disks as a means of disassociating a "low cost" expectation from RAID technology.[2]
"RAID" is now used as an umbrella term for computer data storage schemes that can divide and replicate data among multiple hard disk drives. The different schemes/architectures are named by the word RAID followed by a number, as in RAID 0, RAID 1, etc. RAID's various designs all involve two key design goals: increased data reliability or increased input/output performance. When multiple physical disks are set up to use RAID technology, they are said to be in a RAID array. This array distributes data across multiple disks, but the array is seen by the computer user and operating system as one single disk. RAID can be set up to serve several different purposes.
Message edited by randomizer on 07-13-2009 at 06:10:17 AM
Lightning strikes nearby, killing my ASUS P4B800E Deluxe MB and leaving me trying to recover data files from the two serial drives setup as raid-0. I would like to simply add the drives to my media PC, which uses a Gigabyte GA-8N-SLI Pro MB. This means moving from the Intel ICH5R to the NVIDIA raid controllers. Will this work and can anyone offer insights/suggestions. thanks
Hi
I have 300GB*4 SATA hard disk , I have planned to create RAID 10, If I create RAID 5 means without Hotswap, I will get 900GB space. If I have done RAID 10 means how many space I will get? Pls share your ideas........
| steve54 wrote : Lightning strikes nearby... |
If you have lightning issues you may want to opt for off-site/cloud storage.
I want to upgrade my C drive to a mirrored pair.
I've been using an IDE drive as my C drive on Windows XP Pro. I bought two 1TB SATA drives, which I would like to use mirrored, as RAID1. I would like these drives to function as the C drive, if this is possible. My Mobo is a Biostar P4M4900-M7 SE with a VIA controller.
I see the Bios setting for RAID, but I don't know what Raid levels it supports. I'm not sure of the procedure for setting up the new drives, getting the right drivers installed, and getting the system to boot with the RAID drives.
I have Partition Manager, and I've already copied my old C drive contents to one of the SATA drives. Do I need to replicate it on the second drive before setting them up as mirrored? And then what?
Is there a good tutorial for this?
My computer does have a floppy drive, if that is needed for installing drivers.
Thank you,
Scott
Got a question: I got 3 x 100 gig hdd setup in raid 0, for a 300gb volume.... now question is each drive has 8 meg cache,,, so now do i had 24 meg cache,,,or do drives just use one 8 meg cache,,, can someone please explain this one to me,,thank you
should i format and partition the HDD first, then configure RAID?
OR configure RAID, then format and partition the HDD second?
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